Port to gfx-rs
Merge pull request #70 from cmr/gfx

Port to gfx-rs
minecraft: NBT decoding.
minecraft: implement simple loading of Anvil region files and chunk columns.
minecraft: dump biome and block state data from 1.8-pre1.
texture: add ColorMap, that maps 2D byte coords to colors from a 256x256 triangle.
minecraft: biome grass/foliage color loading.
texture: add a progressive AtlasBuilder for fixed-size textures.
minecraft: block state and model loading.
Render minecraft chunks.