/**
  * Creates a new instance of this class if one hasn't already been made
  * and then returns the single instance of this class.
  *
  * @return RegenerateThumbnails
  */
 public static function instance()
 {
     if (!isset(self::$instance)) {
         self::$instance = new RegenerateThumbnails();
         self::$instance->setup();
     }
     return self::$instance;
 }