irc: Refactor using (8sync contrib irc) library from Snuik.

irc: Refactor using (8sync contrib irc) library from Snuik.

Switch to new IRC library while retaining 0.4.2 api compatibility.

* 8sync/systems/irc.scm: Rewrite using low level irc functions
from (8sync contrib irc).
(irc-socket-setup): Remove,
(<irc-bot>): Update to use %irc:default-port.  Add dispatch-message
handler.
(irc-bot-init): Refactor using irc:listen, irc:user, irc:nick.
(irc-bot-main-loop): Dispatch to...
(dispatch-message): ...this new message handler.
(handle-message): New overridable handler.  Invoke legacy
handle-misc-input and handle-line handlers for PRIVMSG.