also:
- fixed a bunch of doxygen parsing issues
- added `#define` leak detection to the single-header script
- renamed `TOML_ALL_INLINE` to `TOML_HEADER_ONLY` (the old one still works too)
- simplified abi namespace definitions
also:
- added ability to construct values from wide strings and u8 strings
- added non-template version of array::is_homogeneous()
- added explicit instantiations for more template types when `!TOML_ALL_INLINE`
- cleaned up abi namespaces
- simplified build and test machinery on windows
- removed TOML_CHAR_8_STRINGS since it no longer makes sense
