[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
@nkt Contrary to your opinion I consider omitting `@return void` a bad practice. And because there are two distinct schools of thought here the standard supports both schools. It is perfectly valid to omit `@return` (but I _personally_ do not recommend it) and it is perfectly valid to use `@return void`.