release 2.3.0

fixed parser memory leak (fixes marzer#64)

also:
- build/infra improvements
- updated submodules
- updated conformance tests
- misc code review/refactors
- library version bump
- TOML version bump

Update README [skip ci]

deprecated parse_result::get() in favour of parse_result::table()

also:
- fixed static assert messages being badly formatted on clang
- minor documentation fixes
- updated version numbers

refactoring parser to reduce binary sizes

Basically boils down to eliminating excessive template instantiations.

fixed single-digit negative integer parsing bug (closes marzer#39)

also:
- fixed overflow for very long binary integer literals
- added optimization for parsing string views containing trailing null characters
- added more tests

fixing typo (marzer#26)

minor improvements to the wording of some error messages

also:
- added 'error_printer' example

refactored parser

Mainly to simplify a the error handling code (it had gotten a bit verbose), but also to reduce compiled binary sizes.

also:
- moved windows terminal code page stuff in examples to a separate file