/**
  * Returns the request handler (Guzzle client for the moment).
  * Creates and setups handler if not set.
  * @return Handler
  */
 public function getHandler()
 {
     if (static::$_handler === null) {
         static::$_handler = new Handler($this->config);
         static::$_handler->setUserAgent('hiart/0.x');
     }
     return static::$_handler;
 }