zufast 0.1.0

• Initial CRAN release: a header-only library of small, fast, portable C99 primitives, used by other packages through LinkingTo: zufast alone.
• zufast/number.h: correctly rounded parsing of double, float and 32/64-bit integers in any base 2 to 36 (with a JSON mode), through the vendored ffc.h, a C port of fast_float; shortest round-trip formatting in ECMAScript notation through the vendored Ryu; exact fixed-notation formatting and integer writers.
• zufast/datetime.h: ISO 8601 / RFC 3339 date and timestamp parsing to fields, calendar arithmetic exact over the whole int32_t day range, and RFC 3339 formatting.
• zufast/literal.h (booleans with per-spelling flags, literal matching, ASCII whitespace), zufast/uuid.h, zufast/hex.h and zufast/base64.h (strict, standard and URL alphabets), zufast/hash.h (XXH3 64- and 128-bit, one-shot and streaming, through the vendored xxHash), zufast/bits.h (binary16, bfloat16, endian helpers) and zufast/utf8.h (UTF-8 validation and code-point counting).
• R functions that exercise the C layer: fast_parse_double(), fast_parse_integer(), fast_format_double(), fast_parse_date(), fast_parse_datetime(), fast_datetime_fields(), fast_format_datetime(), fast_hex_encode(), fast_hex_decode(), fast_base64_encode(), fast_base64_decode(), fast_hash(), fast_utf8_valid() and fast_info().
• vignette("linking") gives the consumer recipe.