code: func NewMessageToChannel(username string, text string) MessageConfig {
  	return MessageConfig{
  		BaseChat: BaseChat{
  			ChannelUsername: username,
  		},
  		Text: text,
  	}
  }
docs: // NewMessageToChannel creates a new Message that is sent to a channel
  // by username.
  //
  // username is the username of the channel, text is the message text.