Updated information surrounding the usage of `optional` and the `--experimental_allow_proto3_optional` flag with relevant information between v3.12 & 3.15.
Since release v3.15:
> Optional fields for proto3 are enabled by default, and no longer require
> the --experimental_allow_proto3_optional flag.
* Fix a typo
* Fix lots of spelling errors
* Fix a few more spelling mistakes
* s/parsable/parseable/
* Don't touch the third party files
* Cloneable is the preferred C# term
* Copyable is the preferred C++ term
* Revert "s/parsable/parseable/"
This reverts commit 534ecf7675.
* Revert unparseable->unparsable corrections
This includes instructions for enabling explicit presence tracking in proto3, and also explains implicit presence. The language examples were written by inspection, and not individually tested.
Mitchell Macpherson
Adam Cozzette
Bu Sun Kim
Damien Neil
Joshua Haberman
Peter Newman
listonjesse
Greg Steuck
David L. Jones