(bug 38492) let doxygen document variables

(bug 38492) let doxygen document variables

We are using '@var' to document our variables and class properties,
which is unfortunately not working since '@var' is really meant to
document a function or method.

The way to fix it is to use an input filter that will rewrite our PHP
source code to pretends variables are typed. Aka something like:

 /**
  * A title object
  * @var Title
  */
 var $title;

Will be made:

 /**
  * A title object
  * @var Title
  */
 Title $title;

That is incorrect PHP code but it is properly recognized by Doxygen.

This patch as a side effect, all variables and properties will end up
being documented in addition of type hinting.

Use a hack authored by Goran Rakic at:
	http://stackoverflow.com/a/8472180/276152

Change-Id: I4ead1bd1feace44496b45ed8c55f5e52c59e7694