pybox2d svn up until r50

(pictured: test_TheoJansen.py running on the Pyglet 1.1 testbed)

Recent changes up to r50:

setup.py: Allow for CXXFLAGS to be used (OS X -> Universal Binaries, Linux -> x64) (r47)
TestSegment works (thanks for the tip, neonnds!) (r35)
Backported the testbed to pyglet 1.1. (r50)
test_BreakableBody and TriangleMesh added (thanks nimodo!) (forum post)
OS X guide added (thanks neonnds!)
Added more comments, documentation, fixes. Various cleanups.

Everything should now be updated to Box2D r172 (r162 typo in commit log), with new Step function and slingshot in the testbed.