Chunks too far away should not be rendered

[Jesse-V]

A spherical world of the size we should have is too large to be rendered at a decent FPS, even if it's a thin hollow sphere. The world should be divided up into chunks. If a chunk's boundaries are too far away from the camera, it should not be rendered. Perhaps a helper thread could run and update a "visible" flag on the chunk. This would greatly speed up rendering. Might be a good idea to hold 32^3 cubes in a chunk or so.