/**
  * Returns singletonian instance of this class.
  *
  * @return Ai1ec_Seo_Helper Singletonian instance of self
  */
 public static function get_instance()
 {
     if (!self::$_instance instanceof Ai1ec_Seo_Helper) {
         self::$_instance = new Ai1ec_Seo_Helper();
     }
     return self::$_instance;
 }