[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
... elements MUST their usage be restricted...
===>
... elements, their usage MUST be restricted...

Also, what are "locations" in this sentence? I think that inline phpdoc is restricted to use in tags, right, and they are always part of documentation? So maybe take out "and locations that are documented" at the end of this sentence?

Actually... What kind of confusion is this preventing? The above says you can use inline PHPdoc for tags... maybe this whole sentence should be removed? I don't think it is really telling me anything?