Refactor: inline internal function call
Make send_ircmsg() public
Reply to the source of the PRIVMSG instead of the channel we camp

The source is the channel currently, but it might be something else in
the future if add support for multiple channels and/or private
conversations.
Make admin_check() public
Make Bot.nick a readonly property
Use RX callbacks to handle PING/PONG
Use RX callbacks to handle ERROR
Use RX callback to handle 001
Use RX callbacks to handle PRIVMSG
Add dedicated functions for sending NICK, USER and QUIT messages
jotain