completely overhauled models framework...
now loads Model, Mesh, Material, and Texture (plus TextureFile)
fixed a number of bugs/inflexibilities in gamedata xml parser
refactored the various modules to use "init" functions to better control when they get loaded (ie, before or after OpenGL init)
which it turns out is *very important*, because if the shaders and textures get loaded before OpenGL does, they don't work. go figure.
