Tests refactor

This breaks the toml files used for tests into separate files. This way other projects might be able to use those files without having to extract them from the Python tests. I had created these tests for my own pytoml implementation based on pyparsing. However, when I saw yours, I figured I'd just integrate my tests into your project.

These tests uncovered what I believe to be a couple bugs:
* Keys can start with or consist entirely of numbers (see [#65](https://github.com/mojombo/toml/issues/65)). This hasn't entirely been decided but it will be good to have tests either way.
* Single quoted strings cannot contain escaped single quotes and the same for double quotes.