Added a new stone texture. Though, it's not being used now.
Reduce memory used by the sunlight lighting buffer.

Reduce the size of the sunlight lighting buffer to the bare minimum needed
to interpolate light without errors. A larger buffer is used temporarily
during sunlight propagation and is then discarded.

This reduces the game's malloc high-water mark from 232MB to 98MB. Steady-
state malloc memory use also drops from 145MB to 67MB.
Sunlight data is saved using the Dispatch I/O API.

This will help prevent blocking dispatch queues.
GSLightingBuffer loads the lighting buffer using the Dispatch I/O API.
GSChunkVoxelData saves voxel data using the Dispatch I/O API.
GSChunkVoxelData loads voxel data using the Dispatch I/O API.
GSChunkGeometryData saves geometry data using the Dispatch I/O API.