Start connections as temporary children

Since the default API offered by ExIRC does not name connection
the way to access them is via a PID.
Having the supervisor be a :transient one means that in case the
connection would die, it would be restarted by the supervisor.
But since we only ever knew the PID, we have no way to refer back to
this newly restarted process and thus a zombie process is roaming
the VM.

Closes #49