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
also:
- fixed some parsing and printing ops being locale-dependent (fixes#19)
- fixed pkgconfig subdir being wrong (fixes#23)
- fixed some parsing errors at EOF when `TOML_EXCEPTIONS = 0`
- fixed some unreferenced variable warnings on older compilers
- fixed some 'maybe-uninitialized' false-positives on GCC9
- added debug/release awareness to CI tests
- added locale awareness to catch test runner