code: func (rtm *RTM) SendMessage(msg *OutgoingMessage) {
  	if msg == nil {
  		rtm.Debugln("Error: Attempted to SendMessage(nil)")
  		return
  	}
  
  	rtm.outgoingMessages <- *msg
  }
docs: // SendMessage submits a simple message through the websocket.  For
  // more complicated messages, use `rtm.PostMessage` with a complete
  // struct describing your attachments and all.