rm boost/{format,foreach}; reduce #includes; small fixes
remove boost/unordered_map; fix comment formatting
move Gosu backend into its own directory
finish move to Python-handled imports

Builds on Mac. Makefile is broken on Linux.

Things currently broken:
 * creating Script object from PyObject
   (ergo, AI is broken)
 * pausing music from script
   (not new, this happened with the move to Music singleton)