IRCv3 away-notify capability
Neat lightweight notifications of the awayness of contacts.
In practice, this means weechat/hexchat users can see away people in
their nick list and change show_users to 'online,special,away' to avoid
the mode spam completely.
These are also sent on online/offline changes, since offline_user_quits
can be turned off, and you'd need something when they come back.