Travis PR build notifications on Slack and IRC

[Edward Z. Yang]

Hello all,

I'm happy to announce that you can get IRC and Slack notifications
for Travis builds on https://github.com/haskell/cabal .  This should
make it more convenient to submit pull requests as you can get
pinged when the build is finished.

IRC notifications are only for branches on the main haskell/cabal
repository (not PRs; this is a limitation of Travis's IRC integration)
and can be subscribed to by joining ##haskell-cabal on freenode.net

I would not have setup Slack notifications, except between Slack and
HipChat this is the only way to get Travis to send per-PR messages at
the moment.  Slack notifications are on the haskell-cabal Slack team,
and also include build notifications for PRs.  The free tier requires
explicit signups so I've deployed a small app
https://haskell-cabal.herokuapp.com/ to automatically issue invites;
just type in your email and it will give you an invite to the Slack
channel. (Courtesy of https://github.com/outsideris/slack-invite-automation)
The Travis bot posts to #travis.  I personally am connected to Slack
over the IRC bridge; Google for setup instructions.

If you would like to be added as an admin for the Slack instance please
let me know and I'll add you.  I've also added this information
to the Cabal wiki front page: https://github.com/haskell/cabal/wiki

Edward