Changed references from PBox2D to Box2DProcessing or Box2D-for-Processing
Merge pull request #21 from liam-middlebrook/rename/PBox2D

Changed references from PBox2D to Box2DProcessing or Box2D-for-Processing
Fix reset in live examples (on natureofcode.com)

- Dispose previously running sketch before starting one when `RESET` is pressed.
- Update `PAUSE` button label according state (i.e. `RESUME` when is paused, `PAUSE` when is not).

Fix shiffman/The-Nature-of-Code#25