Just "loading" and "unloading" (both really just hints due to the
caching system), and an internal function for converting a handle to a
model pointer, but it let me test IQM loading and unloading in Vulkan.
I've run into a bit of an issue with transform management (really, just
need to make them owned by the scene, but that means creating a scene
for quake and quakeworld).
And create rua_game to coordinate other game builtins.
Menus are broken for key handling, but have been since the input rewrite
anyway. rua_input adds the ability to create buttons and axes (but not
destroy them). More work needs to be done to flesh things out, though.
