Add ChefSpec matchers in libraries.

Hopefully short and sweet, added as recommended by [ChefSpec](https://github.com/sethvargo/chefspec#packaging-custom-matchers).

Thanks again for your sweet cookbook, a joy to use!

![765](https://cloud.githubusercontent.com/assets/261548/3970411/104bae0a-27ca-11e4-85d9-7964214c53c3.gif)