Add documentation

[PGLongo]

I have seen in #24 that the library should works with CocoaPods, if its' true you should consider to remove the documentation from the readme and add a link to CocoaDocs that generate automatically the docs for you.

Otherwise you can manually add the documentation using Jazzy

[pNre]

Actually the library does not work with CocoaPods.
The pod is an artifact from the Xcode 6.0 beta times.
Anyway, this is also something we need to do once the support for public extensions in Swift is added to Xcode.