Convert turnip to feature specs

It's time to say goodbye to Turnip. Was a fun experiment, but ultimately the cucumber-style features just weren't doing much for the project other than adding an additional layer of cruft for the test suite. This PR converts them to RSpec Features via Capybara.

I estimate the amount of rejoicing to be...
![St3G0](https://f.cloud.github.com/assets/724/187725/5be7c2c2-7d85-11e2-9afd-a47dd49a2a0b.gif)