added: Rectangle.aabb

* Calculates the Axis Aligned Bounding Box (or aabb) from an array of points.
*
* @method Phaser.Rectangle#aabb
* @param {Phaser.Point[]} points - The array of one or more points.
* @param {Phaser.Rectangle} [out] - Optional Rectangle to store the value in, if not supplied a new Rectangle object will be created.
* @return {Phaser.Rectangle} The new Rectangle object.
* @static
Loader can now natively load XML files via `load.xml`. Once the XML file has loaded it is parsed via either DOMParser or ActiveXObject and then added to the Cache, where it can be retrieved via `cache.getXML(key)`.

Cache now has support for XML files stored in their own container. You can add them with `cache.addXML` (typically this is done from the Loader automatically for you) and get them with `cache.getXML(key)`. There is also `cache.checkXMLKey(key)`, `cache.checkKeys` and `cache.removeXML(key)`.
Merge pull request #1199 from codevinsky/feature/rectangle-aabb

Rectangle.aabb
readme update.
Split the methods and properties into public, protected and private sub-arrays.
Fixed missing Pixi from class names and extends.
Fixing jsdoc headers.
More rigid corruption checks for the pixi docs.
jsdoc fix
docgen updates