* 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.
* Added Windows build instructions to Building.md and added a
"make mingw" command to cross-compile the Windows binary into
the bin/ folder.
* Fix a bug in the Wallpaper texture loader where it would error out
when caching textures to disk the first time.
