code: func (r *Response) Xml(obj interface{}) error {
  	res, err := xml.Marshal(obj)
  	if err != nil {
  		return err
  	}
  
  	r.writer.Header().Set("Content-Type", "application/xml")
  	return r.Raw(res)
  }
docs: // Will produce XML string representation of passed object,
  // and send it to client