/**
  * Return an instance of this class.
  *
  * @since	 1.0.0
  *
  * @return	object	A single instance of this class.
  */
 public static function get_instance()
 {
     // If the single instance hasn't been set, set it now.
     if (null == self::$instance) {
         self::$instance = new self();
     }
     return self::$instance;
 }