* Add a Red Azulian as a test for mobile enemies.
* Its A.I. has it walk back and forth, changing directions when it
comes up against an obstacle for a few moments.
* It plays walking animations and can trigger collision events with
other Doodads, such as the Electric Door and Trapdoor.
* Move Gravity responsibility to the doodad scripts themselves.
* Call `Self.SetGravity(true)` to opt the Doodad in to gravity.
* The canvas.Loop() adds gravity to any doodad that has it enabled.
* Add some encoding/decoding functions for binary msgpack format for
levels and doodads. Currently it writes msgpack files that can be
decoded and printed by Python (mp2json.py) but it can't re-read from
the binary format. For now, levels will continue to write in JSON
format.
* Add filesystem abstraction functions to the balance/ package to search
multiple paths to find Levels and Doodads, to make way for
system-level doodads.
