# eulerr 8.1

## Highlights

This version brings rotated rectangles as a new shape to eulerr, as well as the
ability to customize the optimizer used to fit the diagram. eulerr is also
parallelized now, and because the fitting pipeline now runs the full fit in
several branches (in parallel), this should bring significant speedups for
larger diagrams.

## Features

- **plotting:** add configurable canvas margin ([`eea3542`](https://github.com/jolars/eulerr/commit/eea354295936f8409debb4914c1d33f9878b94aa))
- support rotated rectangles and configurable optimizers ([`330e42b`](https://github.com/jolars/eulerr/commit/330e42b6c87226cbc3833c3e99869fe1a7a971c3))
- add `n_threads` option for parallelizing fits ([`845a54f`](https://github.com/jolars/eulerr/commit/845a54fb53034be8aecde65ee5a0cedbe31d8c29))
- add `transform` option to fitter ([`f4b99c1`](https://github.com/jolars/eulerr/commit/f4b99c16d10baf5e23263aa81f6ae6efff06dab0)), closes [#96](https://github.com/jolars/eulerr/issues/96)

## Bug fixes

- **plotting:** increase margin around plot to 2 pt ([`3ff50c6`](https://github.com/jolars/eulerr/commit/3ff50c68c204470e5ba2fa6ea0ff486047928a6b))
- note correct rustc requirement in DESCRIPTION ([`9b05074`](https://github.com/jolars/eulerr/commit/9b0507423c6088c1432390b9b44f448d52351a88))

# eulerr 8.0

This is a major milestone for eulerr. The 8.0.0 release introduces a complete
rewrite of the underlying C++ codebase, now relying instead on the Rust library
[Eunoia](https://eunoia.bz), which is a library I have developed. Here are some
of the highlights this brings:

- We have added support for squares and rectangles too!
- Eunoia uses analytical gradients for all the smooth loss functions, which
  leads to significantly improved performance. We have also swapped the default
  optimization algorithm to a Levendberg--Marquardt (LM) method plus CMA-ES
  fallback. The LM method is invoked only when the loss is squared residuals,
  but is then much faster than the previous `nlm()` method. The CMA-ES fallback
  replaces the previous use of the **GenSA** package, and is invoked whenever
  the LM method reaches a minimum that's above a level of error (configurable by
  the user).
- There are now several labeling algorithms that ensure labels do not overlap
  each other or other parts of the diagram.
- As a result of the above, we have been able to drop multiple dependencies:
  **Rcpp**, **RcppArmadillo**, **GenSA**, **polylabelr**, and **polyclip** are
  all no longer required, since **rextendr** and Eunoia handle the Compiled code
  and algorithms natively.
- The calculated intersections are now *sparse*, which means that only the
  intersections that actually appear in either input or output (the diagram) are
  calculated and stored. This is a **breaking change** because it means that you
  cannot index the intersections by their position or intersection name and
  guarantee that you will get a value. Instead, you must check if the
  intersection exists first, and then implicitly it will have a value of zero.
  But this allows eulerr to handle much larger combinations, since we never
  store a `2^n - 1`-sized vector anywhere.

## Breaking changes

- return sparse residuals
  ([`decc985`](https://github.com/jolars/eulerr/commit/decc9856f7894296024af3b032f1f056800690ae))

## Features

- add square and rectangle shapes
  ([`44c9a1a`](https://github.com/jolars/eulerr/commit/44c9a1afb622bf279279a6369c142e4b753b96c3))
- **plotting:** add placement strategies for labels
  ([`308167a`](https://github.com/jolars/eulerr/commit/308167a599aa0f9a9ac9e7ee6aa780ecbcb6642f))
- add `annotations` argument for annotating intersections
  ([`19d2d87`](https://github.com/jolars/eulerr/commit/19d2d877cf8b41a5521944531e211e65f82a31b0)),
  closes [#70](https://github.com/jolars/eulerr/issues/70)
- add plot composing via `+`, `/` and `|`
  ([`d974c08`](https://github.com/jolars/eulerr/commit/d974c0826d455111dcc7b267477a347898549753)),
  closes [#46](https://github.com/jolars/eulerr/issues/46)
- expose `gap` and separate labels by gap and tether
  ([`17802a2`](https://github.com/jolars/eulerr/commit/17802a2459d6ff7bc779205325a47fa2f197a62a))
- add `template` to `quantities` in `plot()`
  ([`59ddd71`](https://github.com/jolars/eulerr/commit/59ddd71e464978dda91786ca74b3b589a63deb34)),
  closes [#99](https://github.com/jolars/eulerr/issues/99)
- employ Eunoia's label-placement framework
  ([`4ed75b4`](https://github.com/jolars/eulerr/commit/4ed75b483c4bf88df50d23451ed2c142c2d24af3)),
  closes [#69](https://github.com/jolars/eulerr/issues/69) and
  [#4](https://github.com/jolars/eulerr/issues/4)
- add complement
  ([`b6ce232`](https://github.com/jolars/eulerr/commit/b6ce23280d4b54b932659f2ce9c73c5df59f5be7)),
  closes [#13](https://github.com/jolars/eulerr/issues/13)
- add new loss functions, deprecate old and `loss_aggregator`
  ([`03e7dea`](https://github.com/jolars/eulerr/commit/03e7dea3c813676ee87418a1ef52667f498df4e6))
- add `max_sets` in `control` for capping max sets
  ([`621a898`](https://github.com/jolars/eulerr/commit/621a898f1e523df8f5d904a3543bb35dd1355ff8)),
  closes [#85](https://github.com/jolars/eulerr/issues/85)
- add `by_groups` to `plot()` for panel-specifics
  ([`f2d5533`](https://github.com/jolars/eulerr/commit/f2d5533d594e0b920042a8b0906a39c0994661b0)),
  closes [#125](https://github.com/jolars/eulerr/issues/125)
- return sparse residuals
  ([`decc985`](https://github.com/jolars/eulerr/commit/decc9856f7894296024af3b032f1f056800690ae))
- update euonoia to 0.8.0
  ([`ceb3138`](https://github.com/jolars/eulerr/commit/ceb313841164760db83a2ac61796fbe9d15125c9))
- update eunoia
  ([`530fb11`](https://github.com/jolars/eulerr/commit/530fb11ad92b52d8a33d8ed6127bf111df95ffeb))
- lower default tolerance
  ([`6400fae`](https://github.com/jolars/eulerr/commit/6400fae1f2575542ece0871acf9198a34d00b4ff))
- **plotting:** add `symbol_size` to configure legend symbol
  ([`1491a49`](https://github.com/jolars/eulerr/commit/1491a494d6fb4d722279fe5d1478dfcb8a792c53)),
  closes [#60](https://github.com/jolars/eulerr/issues/60)
- **plotting:** add `rotate` parameter
  ([`706735c`](https://github.com/jolars/eulerr/commit/706735cce7bbfbdf41165f0623a1f5221aaa471e)),
  closes [#12](https://github.com/jolars/eulerr/issues/12)
- **plots:** support `top` and `left` for labeling strips
  ([`c1a87fb`](https://github.com/jolars/eulerr/commit/c1a87fb68f41dabda740095bd56adef7b2ec937b)),
  closes [#123](https://github.com/jolars/eulerr/issues/123)

## Bug fixes

- add padding to avoid clipping plots
  ([`5129054`](https://github.com/jolars/eulerr/commit/51290543279b843eb03a1b0e8581c43a795fde03))
- use `stats` namespace
  ([`72df9c8`](https://github.com/jolars/eulerr/commit/72df9c81b03cf13672e46d48cb3406ae0e866e14))

## Performance improvements

- upgrade to eunoia 0.11.0
  ([`021ceb4`](https://github.com/jolars/eulerr/commit/021ceb43bd4435b3c108995cc787b69cd9cb8cc5))

# eulerr 7.1

## Features

- allow setting plot options via named vector
  ([`3b7a32e`](https://github.com/jolars/eulerr/commit/3b7a32e945931171f86b1716a47d47807453d9f9)),
  closes [#111](https://github.com/jolars/eulerr/issues/111)
- implement patterns
  ([`caf1c76`](https://github.com/jolars/eulerr/commit/caf1c76dd7c07c24b4f88d114a5d7fac9ab8844d)),
  closes [#83](https://github.com/jolars/eulerr/issues/83)
- set venn diagram class to `venn_eulerr`
  ([`244a657`](https://github.com/jolars/eulerr/commit/244a65758129b75156ada498039baf8b5d47c9db)),
  closes [#78](https://github.com/jolars/eulerr/issues/78)
- add `quantities$format` for number formatting
  ([`b01e69b`](https://github.com/jolars/eulerr/commit/b01e69b8072ea0d45aed27dc74c2a04d09fc2c28)),
  closes [#75](https://github.com/jolars/eulerr/issues/75)
- allow rounding numbers
  ([`6e297a5`](https://github.com/jolars/eulerr/commit/6e297a5b84c63cec0595c38ec1e235be572cda33)),
  closes [#76](https://github.com/jolars/eulerr/issues/76)
- add `bg` option for `plot.euler()`
  ([`bf70290`](https://github.com/jolars/eulerr/commit/bf70290b94e40dc0cf7fd09ba86dbcd29c8adc55)),
  closes [#74](https://github.com/jolars/eulerr/issues/74)
- allow named labels in `quantities`
  ([`4c7d091`](https://github.com/jolars/eulerr/commit/4c7d091d78f286fbdc8a73cacfbeabedaaddeb4a)),
  fixes [#112](https://github.com/jolars/eulerr/issues/112)
- allow expression vectors in `plot.euler()` + `labels`
  ([`cea5e43`](https://github.com/jolars/eulerr/commit/cea5e43313ea1730035d37f0d08b6dc21f8a3623)),
  closes [#118](https://github.com/jolars/eulerr/issues/118)

## Bug fixes

- strictly map colors to set identities
  ([`a58fce5`](https://github.com/jolars/eulerr/commit/a58fce5f44decf449bad6fb3a4d54c041f888d5b)),
  closes [#109](https://github.com/jolars/eulerr/issues/109)
- use correct number of columns in tabular
  ([`4880f5e`](https://github.com/jolars/eulerr/commit/4880f5ebeeebd381665df3affad6841e3dbdd401)),
  closes [#116](https://github.com/jolars/eulerr/issues/116)

# eulerr 7.0.4

## Bug Fixes

- Ignore `air.toml` in `Rbuildignore` to fix R CMD check warning.

# eulerr 7.0.3

## Bug Fixes

- Fix deprecated use of `arma::is_finite()` in C++ code.
- Fix URL link to eulerAPE in documentation.
- Fix URL link to workshop paper in documentation and citation.

# eulerr 7.0.2

## Bug Fixes

- Fix order and layout of strips when grouping (#108, by @altairwei)

# eulerr 7.0.1

## Minor Changes

- Fixed some incorrect documentation of internal functions.
- Corrected an url for eulerAPE.

# eulerr 7.0.0

## New Features

- It is now possible to set the loss function to be used when trying to optimize
  the Euler diagram layout via `loss` and `loss_aggregator`. There is a new
  vignette that showcases this new feature.

## Minor Changes

- C++14 is now required for the package.

## Bug Fixes

- Label repelling via `adjust_labels` in `plot.euler()` has been deprecated and
  removed to fix sanitizer warnings.

# eulerr 6.1.1

## Minor changes

- citation to conference paper added to `inst/CITATION`
- error messages for erroneous input have been improved in several places
- switched `PI` to `M_PI` to support `STRICT_R_HEADERS` in C++ code (#82, thanks
  @eddelbuettel)

## Bug fixes

- error in documentation for list method has been fixed, thanks @gprezza (##77)

# eulerr 6.1.0

## Minor changes

- Label repelling (activated by calling `euler()` with `adjust_labels = TRUE`)
  no longer repels text labels away from the edges of the shapes in the diagram.

## Bug fixes

- Rectify sanitizer error from clang-ASAN test environment.

# eulerr 6.0.2

## Bug fixes

- Set `stringsAsFactors = TRUE` inside all relevant functions in `euler()` to
  avoid errors in upcoming R version.
- Fix broken link in *eulerr under the hood* vignette.

# eulerr 6.0.1

## Minor changes

- Throw an error message when the number of sets in `venn()` exceeds 5 (##65)
- Performance improved when large lists are used as input to `euler()` and
  `venn()` (##64, @privefl)

## Bug fixes

- Correctly handle `data.frame` inputs to `euler()` when categorical variables
  are character vectors and not factors.

# eulerr 6.0.0

## New features

- In `plot.euler()`, percentages can be added to the plot in addition to or
  instead of counts by providing a `list` to the `quantities` argument with an
  item `type` that can take any combination of `counts` and `percent`. This
  change also comes with a redesign of the grid graphics implementation for
  labels.
- `eulerr_options()` gains a new argument `padding` which controls the amount of
  padding between labels and quantities. (##48)
- `plot.euler()` now uses code from the **ggrepel** package to prevent labels
  from overlapping or escaping the plot area if `adjust_labels` is set to
  `TRUE`.
- A new vignette featuring a gallery of plots from the package has been added.

## Minor changes

- The default `cex` for quantity labels has changed from 1.0 to 0.9.
- Labels for sets that overlap are now merged (partly fixes ##45)
- The fill colors for sets which are completely contained within another set are
  now once again composed of a mix of the color of the subset and the superset.
- Plotting data has been exposed in a `data` slot in the object created by
  calling to `plot.euler()` (##57)

## Bug fixes

- An error in layout normalization that occurred sometimes with ellipses has
  been fixed.

## eulerr 5.1.0

## New features

- `venn()` is a new function that produces Venn diagrams for up to 5 sets. The
  interface is almost identical to `euler()` except that a single integer can
  also be provided. A new vignette, *Venn diagrams with eulerr*, exemplifies its
  use.

## Minor changes

- Calculations for the strips in `plot.euler()` when a list of Euler diagrams is
  given has been improved. Setting `fontsize` or `cex` now results in
  appropriately sized strips as one would expect.
- Tiny overlaps (where the fraction of the area is less than one thousandth of
  the largest overlap) in the final diagram are no longer plotted.
- `eulergram()` objects from `plot.euler()` now have a proper grob name for the
  canvas grob, so that extracting information from them is easier.

## Bug fixes

- Return value documentation for `euler()` now correctly says "ellipses" and not
  "coefficients".
- `data.frame` or `matrix` inputs now work properly when values are numerical.
  (##42)
- Fixed some spelling errors in news and vignettes.

# eulerr 5.0.0

## New features

- `error_plot()` is a new function that offers diagnostic plots of fits from
  `euler()`, letting the user visualize the error in the resulting Euler
  diagram.

## Major changes

- `euler()` once again uses the residual sums of squares, rather than the stress
  metric, as optimization objective, which means that output is always scaled
  appropriately to input (##28).
- `plot.euler()` now uses the
  [polylabelr](https://CRAN.R-project.org/package=polylabelr) package to
  position labels for the overlaps of the ellipses, which has improved
  performance in plotting complicated diagrams considerably and reduced the
  amount of code in this package greatly.
- The c++ internals have been rewritten using more memory-efficient, performant
  and expressive code.

## Minor changes

- The `euler.data.frame()` method (and by proxy the `euler.matrix()` method) can
  now take matrices with factors in addition to the previously supported logical
  and integer (binary) input. The function will dummy code the variables for the
  user.
- A few performance fixes.
- Additional unit tests.
- Previously deprecated arguments to `plot.euler()` have been made defunct.
- Added a data set, `plants`, to exemplify the list method for `euler()`.
- Added a data set, `fruits`, to exemplify the data.frame method for `euler()`.
- `euler.data.frame()` gains an argument `sep`, which is a character vector used
  to separate dummy-coded factors if there are factors or characters in the
  input.
- Added a data set, `organisms`, to exemplify the matrix method for `euler()`.
- Added a data set, `pain`, to exemplify the table method for `euler()`.
- `euler.table()` gains an argument, `factor_names`, for specifying whether the
  factor names should be included when generating dummy-coded variables in case
  the input is a data.frame with character or factor vectors or if the input is
  a table with more than two columns or rows.
- Parts of the *eulerr under the hood* vignette has been branched off into a new
  vignette regarding visualization.

## Bug fixes

- Empty combinations can now be provided and will be plotted (generating
  completely blank plots).
- `euler.list()` now passes its ellipsis argument along properly. (##33, thanks,
  @banfai)
- Several spelling and grammar mistakes were corrected in vignettes and
  documentation.

# eulerr 4.1.0

## Minor changes

- `plot.euler()` now returns a `gTree` object. All of the plotting mechanisms
  are now also found in this function and `plot.eulergram()` and
  `print.eulergram()` basically just call `grid::grid.draw()` on the result of
  `plot.euler()`. This change means that functions such as
  `gridExtra::grid.arrange()` now work as one would intuit on the objects
  produced by `plot.euler()`.
- Fitting and plotting Euler diagrams with empty sets is now allowed (##23).
  Empty sets in the input will be returned as `NA` in the resulting `data.frame`
  of ellipses.
- The last-ditch optimizer has been switched back to `GenSA::GenSA()` from
  `RcppDE::DEoptim()`.

## Bug fixes

- The **grid** parameters available for *edges* are now correctly specified in
  the manual for `plot.euler()`.
- `euler.data.frame()` now works as expected for tibbles (from the **tibble**
  package) when argument `by` is used.

# eulerr 4.0.0

## Major changes

- `plot.euler()` has been rewritten completely from scratch, now using a custom
  **grid**-based implementation rather than **lattice**. As a result, all
  `panel.*()` functions and `label()` have been deprecated as well as arguments
  `fill_alpha`, `auto.key`, `fontface`, `par.settings`, `default.prepanel`,
  `default.scales`, and `panel`. The method for plotting diagrams has also
  changed---rather than overlaying shapes on top of each other, the diagram is
  now split into separate polygons using the **polyclip** package. Instead of
  relying on semi-transparent fills, the colors of the fills are now blended in
  the CIELab color space (##16).
- The default color palette has been redesigned from scratch to suit the new
  plot method.
- A new function `eulerr_options()` have been provided in order to set default
  graphical parameters for the diagrams.

## Minor changes

- Arguments `counts` and `outer_strips` to `plot.euler()` are now defunct.
- `euler()` now always returns ellipse-based parameters with columns `h`, `k`,
  `a`, `b`, and `phi`, regardless of which shape is used. This item was
  previously named "coefficients", but it now called "ellipses" instead and a
  custom `coef.euler()` method has been added to make cure that `coef()` still
  works.
- Layouts are now partially normalized so that diagrams will look approximately
  the same even with different random seeds.

## Bug fixes

- Providing custom labels to `quantities` and `labels` arguments of
  `plot.euler()` now works correctly (##20).

# eulerr 3.1.0

## Major changes

- The last-ditch optimizer switched from `GenSA::GenSA()` to
  `RcppDE::DEoptim()`.
- The optimizer used in all the remaining cases, including all circular diagrams
  and initial layouts, was switched back to `stats::nlm()` again.
- In final optimization, we now use *stress* instead of residual sums of squares
  as a target for our optimizer.

## Minor changes

- `label` is now a proper generic with an appropriate method (`label.euler()`).
- The **eulerr under the hood** vignette has received a substantial update.

## Bug fixes

- Fixed warnings resulting from the deprecated `counts` argument in one of the
  vignettes.
- Fixed memcheck errors in the final optimizer.
- Corrected erroneous labeling when `auto.key = TRUE` and labels were *not* in
  alphabetic order. (##15)

# eulerr 3.0.1

## Bug fixes

- Added the missing `%\VignetteEngine{knitr::knitr}` to both vignettes. It had
  mistakenly been left out, which had mangled the resulting vignettes.

# eulerr 3.0.0

## Major changes

- Ellipses are now supported by setting the new argument `shape = "ellipse"` in
  `euler()`. This functionality accompanies an overhaul of the innards of the
  function.
- Initial optimization function and gradient have been ported to C++.
- The initial optimizer has been switched from
  `stats::optim(..., method = "L-BFGS-B")` to `stats::nlminb()`.
- The final optimizer now falls back to `GenSA::GenSA()` when the fit from
  `nlminb()` isn't good enough, by default for 3 sets and ellipses, but this
  behavior can be controlled via a new argument `control`.
- A packing algorithm has been introduced to arrange disjoint clusters of
  ellipses/circles.
- The label placement algorithm has been rewritten to handle ellipses and been
  ported to C++. It now uses numerical optimization, which should provide
  slightly more accurate locations.
- The initial optimizer now uses an analytical Hessian in addition to gradient.

## Minor changes

- The initial optimizer now restarts up to 10 times and picks the best fit
  (unless it is perfect somewhere along the way).
- The default palette has been changed to a fixed palette, still adapted to
  color deficiency, but with some manual adjustments to, among other things,
  avoid unnecessary use of color.
- The names of the `diagError` and `regionError` metrics have been changed from
  `diag_error` and `region_error` to reflect the original names.
- The coordinates for the centers are now called *h* and *k* instead of *x* and
  *y*, respectively.
- A new `label()` function has been added to extract locations for the overlaps
  for third party plotting (##10).
- The `counts` argument to `plot.euler()` and `panel.euler.labels()` have been
  deprecated in favor of the more appropriate `quantities`.
- Argument `fill_opacity` in `plot.euler()` that was deprecated in
  [v2.0.0](https://github.com/jolars/eulerr/releases/tag/v2.0.0) has been made
  defunct.

# eulerr 2.0.0

## Major changes

- `eulerr()` has been replaced with `euler()` (see update 1.1.0) and made
  defunct.
- There are two new methods for `euler`:
  - `euler.list()` produces diagrams from a list of sample spaces.
  - `euler.table()` produces diagrams from a `table` object, as long as there
    are no dimensions with values greater than 2.
- `plot.euler()` has been rewritten (again) from the ground up to better match
  other high-level functions from **lattice**. This change is intended to be as
  smooth as possible and should not make much of a difference to *most* users.
- Arguments `polygon_args`, `mar`, and `text_args` to `plot.euler()` have been
  made defunct.

## Minor changes

- `plot.euler()` handles conflicting arguments better.
- c++ routines in `eulerr` now use registration.
- `euler()` now allows single sets (##9).
- Labels in `plot.euler()` now use a bold font face by default in order to
  distinguish them from the typeface used for counts.
- Argument `key` in `plot.euler()` has been deprecated and replaced with
  `auto.key`. Notice that using `key` does not throw a warning since the
  argument is used in `lattice::xyplot()` (which `plot.euler()` relies on).
- Argument `fill_opacity` is softly deprecated and has been replaced with
  `fill_alpha` for consistency with other lattice functions.

## Bug fixes

- `border` argument in `plot.euler()` works again (##7).

# eulerr 1.1.0

## Major changes

- `eulerr()` and its related methods been deprecated and are being replaced by
  `euler()`, which takes slightly different input. Notably, the default is now
  to provide input in the form of disjoint class combinations, rather than
  unions. This is partly to make the function a drop-in replacement for
  `venneuler::venneuler`.
- `plot.euler()` has been completely revamped, now interfacing `xyplot()` from
  lattice. As a result, arguments `polygon_args`, `mar`, and `text_args` have
  been deprecated.

## Minor changes

- Added a `counts` argument to `plot.eulerr`, which intersections and
  complements with counts from the original set specification (##6).
- Added a `key` argument to `plot.eulerr` that prints a legend next to the
  diagram.
- Switched to `atan2()` from RcppArmadillo.
- Added version requirement for RcppArmadillo.
- Dropped dependency on MASS for computing label placement, replacing it with a
  faster, geometric algorithm.
- Dropped the cost function argument `cost` and now forces the function to use
  sums of squares, which is more or less equivalent to the cost function from
  `venneuler`.
- Color palettes in `plot.euler()` now chooses colors adapted to color vision
  deficiency (deuteranopia). With increasingly large numbers of sets, this
  adaptation is relaxed to make sure that colors are kept visually distinct.
- `euler()` now uses `nlm()` instead of `optim(method = "Nelder-Mead")` for its
  final optimization.

## Bug fixes

- The previous algorithm incorrectly computed loss from unions of sets. It now
  computes loss from disjoint class combinations.
- Added missing row breaks in `print.eulerr`.

# eulerr 1.0.0

## New features

- Final optimization routines have been completely rewritten in C++ using Rcpp
  and RcppArmadillo.
- Switched to the cost function from EulerAPE for the default optimization
  target but added the possibility to choose cost function via a `cost` argument
  (currently `eulerAPE` or `venneuler`).
- Added the option to produce conditional eulerr plots via a `by` argument to
  `eulerr`. The result is a list of Euler diagrams that can be plotted in a grid
  arrangement via a new plot method.
- Improved label placement by using a two-dimensional kernel density estimation
  instead of means to calculate label centers.

## Bug fixes and minor improvements

- Cleaned up typos and grammar errors in the *Introduction to eulerr* vignette.
- Added `mar` argument to `plot.eulerr` with a default that produces symmetric
  margins.
- Corrected the implementation of the `stress` statistic from venneuler.
- Switched to Vogel sampling to generate points to choose label positions from.
- Minor clean up and performance fixes all around.
- Added a `print.eulerr` method.
- Updated vignette to cover new features and changes.

# eulerr 0.1.0

- The first release.
