Add syntax highlighting for Swift methods.

So I thought I would get the ball rolling on adding some highlighting for methods and functions. Currently, editing Swift in vim looks a little bland. 

This commit adds highlighting for methods. If this pull request is acceptable, then maybe we can also work on adding highlighting for custom methods, method names inside Classes.

Before Change:


![screen shot 2014-12-14 at 20 14 32](https://cloud.githubusercontent.com/assets/1159146/5430812/fe61cb4c-83cd-11e4-9c7c-26a549574a0b.png)

After Change:

![screen shot 2014-12-14 at 20 13 37](https://cloud.githubusercontent.com/assets/1159146/5430814/055b954a-83ce-11e4-8d84-7150d4915e71.png)