Travis CI integration and a bare bone implementation of unit testing target.

Recently, Travis CI announce the support of [iOS/OS X testing](http://about.travis-ci.org/blog/introducing-mac-ios-rubymotion-testing/).

I once saw @mattt mentioned that 2.0 of AFNetworking should be unit tested.

Since there's now a CI and it aligns with in the future direction of the project, I thought it will be cool to create a bare bone unit testing target for both iOS and Mac OS X and make full use of Travis CI.

The Travis CI integration is based on rake. The reason is mostly because I am not good with bash. I also think that rake is a better idea in the sense that it is less cryptic than rake. But someone could come up with a make version.

Here is a working example of [AFNetworking integrated with Travis CI](https://travis-ci.org/lxcid/AFNetworking/builds/6196876).

P.S. Testing AFNetworking async operation will requires the use of the some tricks.

- https://gist.github.com/lxcid/2586763
- http://www.touch-code-magazine.com/unit-testing-for-blocks-based-apis/