PonyDebugger uses CoreGraphics

PonyDebuger uses CGRectContainsPoint(), CGRectGetMidX(), CGRectGetMidY(), CGRectIntegral(), and CGRectZero, which all fit under the umbrella of CoreGraphics.  However, the podspec currently doesn't note that it needs CoreGraphics, so if your project doesn't include the framework already, you'll get linker errors.

E.G.:
![screen shot 2013-09-26 at 1 32 39 pm](https://f.cloud.github.com/assets/74679/1219920/3eeb3044-26d3-11e3-8a4d-051a013e694b.png)

This adds it under `s.frameworks` in PonyDebugger's 0.3.0 podspec.