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
- added doxygen page for the configuration options
- added SPDX-License-Identifiers around the place
- changed TOML_UNRELEASED_FEATURES default to 0
- simplified ABI namespace machinery
- fixed a number of doxygen bugs
also:
- fixed parser not handling floats with leading '.' characters
- added `TOML_PARSER` configuration option
- added `TOML_LIB_SINGLE_HEADER` indicator
- moved parse_error and the utf8 stream machinery to separate headers
- updated catch2
