Fix travis build matrix

It looks like the build has been broken on this project for a little while (actually forever :grimacing:) now. I went through the process of cleaning up the build matrix, creating custom gemfiles for specific scenarios, and fixing the tests to get a green build on Travis-CI.

**This PR should turn the project green.**

Build matrix includes all the proper permutations of:

* Ruby 1.9.3, 2.0.0, 2.1.0
* Rails 3.2, 4.0, master

I had to make this PR dependent on #22 as well, so pulling this in should auto-close that one too.