Add missing filter documentation

[johnjamesjacoby]

In r6438, I added an easy way to identify which filters are missing documentation blocks.

A search for:

// Filter & return

...currently yields 533 results, all of which represent filters in bbPress that are missing documentation about why someone might want to hook into them.

It would be simply wonderful for some enterprising soul to chug through these and document them. Then we can set bbPress up with one of those fancy auto-documenting filter tools like WordPress has.

Core Trac : ​https://bbpress.trac.wordpress.org/ticket/3110

@JJJ @krupal-panchal Could you please review this.

[SirLouen]

The format is not standard according to Hooks documentation.

Check this:
​https://developer.wordpress.org/coding-standards/inline-documentation-standards/php/#4-hooks-actions-and-filters

There should not be any @return statements, only @param

Also if you have @since in the function, you can take it as a reference.

[johnjamesjacoby]

In 7361:

Tools - Code Improvement: Document some filters.

This commit improves the code documentation of several filters across the codebase.

Props johnjamesjacoby, narenin, sirlouen.

In trunk, for 2.7.

See #3110.

Fixed via: ​https://bbpress.trac.wordpress.org/changeset/7361

Thank you!