Browser tests

It turns out that testing in the browser instead of mocking out localStorage is super crucial, because there's pretty much no way to mock out IndexedDB like I did with localStorage in node. Even if I could, it would be a bad idea, because it would prevent cross-browser testing, which is really important!

I converted the jasmine tests to run in the browser instead of node, and they're all passing in the latest Chrome, Safari, and Firefox. The README has been updated with instructions on how to run the tests.

I had to compile a separate version of backbone.dualstorage.js in the spec/ directory that does not have the wrapper so that I can test/mock the individual components. The README also mentions this and how to build it.