Adds iOS 6.0 Compatibility

Personally I'm not a big fan of supporting dinosaur versions of iOS, but alas, a significant portion of my users are using iPod Touch 4th generations which are limited to iOS 6.0. Seems the only thing missing in iOS 6.0 is the `tintColor` property from `UIView`, so I've created a property which pretty accurately emulates that functionality. I've tested this change on iOS 6 and iOS 7 (and iOS 8, for good measure) and they all seem to work fine. I've even updated your `.podspec` and README for your convenience :smile:.

Apologies for all the pbxproj noise, I regenerated the test project's Pods and CocoaPods saw fit to change just about every line.