Swift syntax highlighting

Extended Flatdoc's highlighting library to include support for swift language. Refer to screenshot attached. Color scheme is based on the Appl's Swift iBook syntax.

Special thanks to @joechee for his help with the regex.

![screen shot 2014-06-10 at 5 15 53 pm](https://cloud.githubusercontent.com/assets/1315101/3227842/f4c8fb3c-f07f-11e3-99fe-23a585a2b0b2.png)