styling helper that supports composite styles and caching

Summarized in the 'Styling' section in the README.md file. I'm pushing this out for review... it would need tests, and improved documentation, but I wanted to see if this is helpful to others.
![settings_screen rb xo-ios 2014-11-14 00-07-00](https://cloud.githubusercontent.com/assets/142875/5041541/a5fa7ec0-6b92-11e4-82a4-73b11b86cdfa.png)