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 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.

The script I had will attempts to color failed tests in red and passed tests in green.

Currently it only test for initialization of AFHTTPClient. Basically the expected way of initializing and when attempts to initialize it with nil, an exception should throws.

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/