Pulled in Mocha for Testing and Sinon for Mocks/Stubs

I'm finally correcting my past mistakes, and starting to build out some tests around thumbd.

I've pulled in Mocha for testing:

http://visionmedia.github.io/mocha/

And Sinon, which is a great library for mocks:

http://sinonjs.org/

I tend to advocate a TDD approach to development now; Going forward it would be nice to:

* Retroactively get tests around key parts of thumbd.
* Make sure to write tests around any new functionality that we build out.