[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
I don't really understand this. If the code looks like
````
/**
 * doc block
 */
$varname = 'initial value';
````
(or the last line might be inside a function, so it might say "global $varname;" instead)

You are declaring a global variable... I do not understand why the @global needs to have the variable name repeated? It seems like if the doc block immediately precedes a variable declaration, and it has @global in it, then it should be an indication that the variable being documented is a global variable. In which case, we should either just have @global with no further information, or use "@global type" as  substitute for @type or @var? Because the doc block itself could have a summary, description, @type, etc. The variable name would not be necessary, since the doc block's Structural Element is the variable, right?

In the second case (usage)... I think you're saying that if the doc block's Structural Element is a function/method, and you are indicating that a global variable is being used inside that function. In that case, it seems like you would just need "@global $name", assuming that the @global tag has been used elsewhere where the global variable is documented. And then this is kind of like a @see reference to the global variable. Alternatively, I guess you could use it to document the global variable, but in that case it would need to be "@global type $name description".