New features

Implements the following 3 features:
- CSS cashing: this helps when a user edits the plugin's CSS file
- Ability to set Font Color
- Ability to set Tile Transparency
- Static Featured Image Overlay

![post-tiles](https://cloud.githubusercontent.com/assets/557102/5158670/311cb8d2-7346-11e4-97e1-03023b36c282.jpg)

- Ability to set the overlay to Peek Title

![post-tiles](https://cloud.githubusercontent.com/assets/557102/5159426/90680268-7366-11e4-940c-160c7b1bbf05.jpg)