/**
  * Access this class's working instance.
  * If the instance hasn't been set, set it now.
  *
  * @wp-hook	void
  * @uses		void
  * @since		2.0.0
  * @return		object of this class
  */
 public static function get_instance()
 {
     if (null == self::$instance) {
         self::$instance = new self();
     }
     return self::$instance;
 }