[DRAFT, WIP] PSR-5: PHPDoc Standard

This PR represents the current state of affairs with the PHPDoc Standard. Until this description and subject is altered this PR is considered a Work in Progress and not ready for a final review.

All feedback is welcome, please direct this to the PHP-FIG mailing list to prevent noise in this PR. This PSR covers so many subjects that unless the discussions are separated by topic that it will probably be quite impossible to follow in this PR.

I would also request that people open a thread per issue they would like to discuss and not combine several issues in a single mail; this will help to keep noise-levels down in discussions and for me to loook back or filter important information.

TODO items are tracked in the issue tracker for this PSR: https://github.com/phpDocumentor/fig-standards/issues
Can we make pull requests since this itself is a pull request? Not sure how to edit...

Recommended places to change:
- Sample doc block in line 132 is promoting @return void. Maybe have a different sample there?
- Same in line 725
- The description of @return around line 1338 says that individual coding standards may only say that @return MAY be omitted. This would put existing Drupal and WordPress coding standards at variance, since both of those say that @return MUST be omitted if there is no return value. So this needs rewording.
- In the section describing type "void" around line 1916, it seems like there could be a note that says that the @return can also be completely omitted in this case.