add a nice 404 page and server tests

![screen shot 2014-10-13 at 12 20 17 pm](https://cloud.githubusercontent.com/assets/2289/4618837/24ced6b2-530e-11e4-8c78-cc896ecb8256.png)

This fixes #7. Add some nice clean server tests using [supertest](https://www.npmjs.org/package/supertest).