all: 0.2-pre commit, read description for full changelog

Biggest change: using function pointers to start and configure threads. And made Barnes-Hut algorithm thread-safe. And rewrote physics_aux. And made the entire program path independent so you can launch it anywhere you want. And install it. There are no hardcoded paths. None. And rewrote the way shaders are loaded. Minor changes: tweaked octree generation and thread distribution functions. Other minor changes: everything I've forgotten. It's still early for 0.2 though, I'll get that out as soon as I finish my goal: fix the octree generation. The key's somewhere in the halfdim root setting. I'm on to ya.