The quake-specific enums are now in the client header, and the particle
system now has a gravity field rather than getting it from
vid_render_data (which I hope to eventually get rid of entirely).
After yesterday's crazy marathon editing all the particles files, and
starting to do another big change to them today, I realized that I
really do need to merge them down. All the actual spawning is now in the
client library (though particle insertion will need to be moved). GLSL
particle rendering is semi-broken in that it now does only points (until
I come up with a way to select between points and quads (probably a
context object, which I need anyway for Vulkan)).