MLib — Useful Standard Library Extensions

MLib is a collection of various headers and libraries that I find useful
in a large enough number of my personal C projects.  This includes for
example: common datastructures, useful non-POSIX APIs, and 21st-century
strings.

This does not aim to be a LibC replacement, but rather a supplimentary
library.  It is a C23 library with no plans to support older standards.

The headers as of now are:
 • alloc.h — memory allocation functions
 • bitset.h — macros for implementing a bitset
 • bob.h — bob the string-builder
 • dynarr.h — macros for implementing a dynamic array
 • errors.h — err.h-inspired diagnostics functions
 • macros.h — miscellaneous utility macros (MIN/MAX/lengthof/etc.)
 • mbstring.h — multibyte-strings
 • rune.h — inttypes.h but for runes

The headers planned for inclusion are:
 • optparse.h — option parsing functions
 • unicode/gbrk.h — grapheme breaking
 • unicode/props.h — unicode character properties