also:
- fixed parser not correctly round-tripping int format in some cases
- added `TOML_ENABLE_FORMATTERS` option
- added `operator->` to `toml::value`
- refactoring
also:
- removed `TOML_LARGE_FILES`
- removed unnecessary template machinery (esp. where ostreams were involved)
- made all overloaded operators 'hidden friends'
- documentation fixes
- version bump - this will form the foundation of v3