Added support for nose+travis testing

I added support for [Travis](http://travis-ci.org) and [nosetests](https://github.com/nose-devs/nose).

I have implemented three tests for Model, but this can be fleshed out in the future. I removed the equivalent code from Model's header. Much of that code seemed to be out of date anyway. 

Travis will need some quick setup on your end (basically logging in with Github and flipping the switch for yahmm). See http://docs.travis-ci.com/user/getting-started/ for more details.

Note: I had some difficulty getting yahmm to compile on both OS X and Linux (Travis runs on Ubuntu boxes). This was due to mingw32 being hard coded as the compiler. I replaced that code with the cross-platform version from Cython's documentation. I don't have a Windows box so I wasn't able to test if it works there. It should work, but it seems like the path to the compiler is hard-coded which seems fragile.

Cheers
-t