code: func (conn *Conn) Topic(channel string, topic ...string) {
  	t := strings.Join(topic, " ")
  	if t != "" {
  		t = " :" + t
  	}
  	conn.Raw(TOPIC + " " + channel + t)
  }
docs: // Topic() sends a TOPIC command for a channel.
  // If no topic is provided this requests that a 332 response is sent by the
  // server for that channel, which can then be handled to retrieve the current
  // channel topic. If a topic is provided the channel's topic will be set.
  //     TOPIC channel
  //     TOPIC channel :topic