code: func timestamp(s ...string) (string, error) {
  	switch len(s) {
  	case 0:
  		return now().Format(time.RFC3339), nil
  	case 1:
  		if s[0] == "unix" {
  			return strconv.FormatInt(now().Unix(), 10), nil
  		}
  		return now().Format(s[0]), nil
  	default:
  		return "", fmt.Errorf("timestamp: wrong number of arguments, expected 0 or 1"+
  			", but got %d", len(s))
  	}
  }
docs: // timestamp returns the current UNIX timestamp in UTC. If an argument is
  // specified, it will be used to format the timestamp.