update code documentation for PSR-5 and WordPress PHP standards

Update documentation for [WordPress PHP documentation standards](http://make.wordpress.org/core/handbook/inline-documentation-standards/php-documentation-standards/) and [PSR-5](https://github.com/phpDocumentor/fig-standards/blob/master/proposed/phpdoc.md).

* Improves documentation of custom filters and actions.
* Adds `@return void` to functions without a return value.
* Adds `@type` documentation of array parameters and return values.

A couple small code fixes thrown in as well:

* Facebook profile link builder was checking for the existence of the `name` key before appending the value of the `username` key; switched the check to `username`.
* Conditional loader of the Facebook section on the profile page was loading the current user object before passing to `user_can()`; changed to a `current_user_can()`