Automate CocoaPods releases

[gfontenot]

We keep forgetting to push the CocoaPods releases. We should automate something when we push tags or something.

[gfontenot]

We could also use that to automate the uploads of prebuilt binaries

[marcelofabri]

@kylef wrote something about this: https://fuller.li/posts/automated-cocoapods-releases-with-ci/

[tonyd256]

I think this would be nice to integrate with CI since we currently don't have CI on the project. I think Circle CI can at least give us Xcode 7.0 support but I was waiting for carthage 9.2 to get into homebrew. Still I weary of any CI and a long term solution. Most CIs have had long waits for Xcode updates.

[paulyoung]

For what it's worth, between http://www.openradar.me/20490378 and http://www.openradar.me/22816454 our CI is basically useless right now.

[gfontenot]

It'd be good to try to roll automated binary releases into this somehow.