Better recognizer behavior & some performance enhancements

Hi there!

I've just made a few changes to the project and thought you might like to test / pull them.

There are 3 things that have changed:

1. A smaller duration for transition (down to .35 from 1)
2. The gesture recognizer now doesn't trigger a push/pop if you make a downward gesture on the bottom half or an upward gesture in the upper half
3. View snapshots are now based on iOS7's new APIs. The performance is increased and the graphics are super clear (in the previous solution the image capture didn't account for screens with a scale of 2 (retina) for example)