Added support for tint color and saturation

Apple's use of blur usually includes two other effects:

1) Tint color. You'll notice their nav bars / tab bars / etc are usually mostly white, with just the strong colors showing through. Current implementation leads the view to always be the color of the view behind it. ![example change](https://f.cloud.github.com/assets/171163/1059697/d1c5f806-11a0-11e3-8f91-a34d485fc122.jpg)

2) Over-saturation. Apple saturates the colors they show through.

Both of these are additional performance hits, but I left them optional for the user. Saturation code pulled from Apple's imageeffect demo from WWDC 2013.