code: func (r *Response) DispatchMessage(m interface{}) error {
  	data, err := json.Marshal(m)
  	if err != nil {
  		return err
  	}
  
  	req, err := http.NewRequest("POST", SendMessageURL, bytes.NewBuffer(data))
  	if err != nil {
  		return err
  	}
  
  	req.Header.Set("Content-Type", "application/json")
  	req.URL.RawQuery = "access_token=" + r.token
  
  	resp, err := http.DefaultClient.Do(req)
  	if err != nil {
  		return err
  	}
  	defer resp.Body.Close()
  	if resp.StatusCode == 200 {
  		return nil
  	}
  	return checkFacebookError(resp.Body)
  }
docs: // DispatchMessage posts the message to messenger, return the error if there's any