iOS 8 Support + High Quality Scaling/Drawing

Added new methods for threading/queues for use on iOS 8+ devices (setThreadPriority: is deprecated in iOS 8).

Set interpolation quality to high when scaling/drawing to remove the jagged edges that would appear before.

Before:
![screenshot 2014-07-23 16 12 10](https://cloud.githubusercontent.com/assets/1368497/3681724/dfe45782-12be-11e4-8849-ede57b6e503e.png)

Now:
![screenshot 2014-07-23 16 11 05](https://cloud.githubusercontent.com/assets/1368497/3681734/f2991a52-12be-11e4-9982-6e5ec330ead8.png)

Original for comparison:
![test](https://cloud.githubusercontent.com/assets/1368497/3681744/132e28ca-12bf-11e4-9c18-83d7adb809a5.png)