moved generic_buffer constructor to source-file
updated gitignore with *.ipch and data/
further implementation of voxel ps
fully (?) implemented voxel pixel shader
big changes f/ vertex-declaration & surface_format

 - vertex-declaration w/ static-cache. raw pointers only please.
 - no longer requires vertex-shader or context on construction.
 - (d3d) CreateInputLayer called lazily inside context when drawing.
 - surface_format_t now known as element_format_t
 - element_count/element_size now used
 - fixes a bug using bitsize instead of bytesize!