Add irc_output to heka

Hrm, I think the timing is wrong on the JoinAndPart stuff here. We're joining right when we put the message on the outqueue, and then we're parting after the message is sent. There's latency before the message actually goes out, what if we get two messages in before the first goes out? When the first message is delivered we'll part the IRC channel, and then we won't be in it when the second message comes up for delivery.

For JoinAndPart to work correctly I think we'll need to join immediately before sending the message, send it, and then immediately part.