TodoMVC spec fixes

Hey, I'm going through some of the test issues. I hope it's okay if I do this iteratively and not in one go.

This addresses how empty new todos are handled, renames `is13` to `isEnter` (which is applicable from the [JS code style guidelines](https://github.com/tastejs/todomvc/blob/master/app-spec.md#code) we have) and removes some trailing spaces in the code.