Added multithreading and fixed step aliasing in renderG, now default render algorithm

The changes from the previous renderF led to a 5-6x speedup on my i5-3570k. The new render method is a fully functional drop-in replacement for renderF. The algorithm is from "A Fast Voxel Traversal Algorithm for Ray Tracing" by John Amanatides and Andrew Woo.

Movement is now framerate-independent, as well.

I also fixed some problems with the repository itself, like checked-in .class files.