doc: update README

refactor: remove needless code snippet

chore: update version

feat: use detail::none_t instead of char

Although the error value from combinators currently does not have any
information, it can have an information because it is a char value. It
is better to use no-information-type explicitly to make it clear that
it does not have any information. So I added none_t in toml::detai and
use it in combinators and parsers as an error value from combinators.

feat: remove deprecated functions

chore: fix typo in README

fix: improve err msg for multiline inline table

show "missing curly brace" instead of "missing table key-value separator"

Merge pull request ToruNiina#52 from ToruNiina/speedup-for-large-files

Speedup parsing large files

chore: fix example of err msg by re-running sample

fix: remove extraneous null character after float

the bug was introduced by snprintf