Remove cxx17 tag. Should rather check for compiler standard support t…

…han forcing 17.

fix `for_each()` for older MSVC

release v3.0.1

Merge branch 'v3'

release v2.5.0

removed `<fstream>` requirement for `parse_file`

also:
- fixed false-positive char_8 support detection on older compilers
- removed extraneous `TOML_API` declarations

release 2.3.0