Add support for Cocoapods for the latest version

[guidomb]

Since we updated the project to use Carthage installing using Cocoapods is broken. We still need to figure out if ReactiveCocoa not being officially supported in Cocoapods is going to be problem for us.

[drdaz]

So I've made pull request #46 which should fix this... it's my first attempt at making a podspec though, so it might need a quick review.