cleanup and beginnings of actual voxels

 - some cleanup in main.cpp
 - voxel.hlsl is the beginnings of SVO traversal
 - node pool still needs to be hooked up to shader, using
   StructuredBuffer(s), still need to figure out C++ side of that.
cleanup of buffers

 - general cleanup of buffer_t
 - adding generic buffers (DX: structured buffers)