Patch 1: Removed several individual mixins and replaced them with base mixins

Hi Jerad,
Thanks for creating a Sass-based style tile implementation. Very nice work. I took the liberty of refactoring several of the individual mixins and replaced them with base mixins. These prototype-style mixins can be reused easily anywhere you need them by simply adjusting the parameters in the mixin call.

Basically what I've done is a DRYing up of the repeated code. You can see an example pen here which uses the new prototype-style mixins:

http://codepen.io/williamdodson/pen/nbiwx

Take a look at the commit log and let me know if you think it would be a good contribution to your project. Thanks again!

William Dodson (@obxdesignworks)