Backport Surfman GL Backend to Hal 0.5#3216

zicklag wants to merge 9 commits intogfx-rs:hal-0.5gfx-rs/gfx:hal-0.5from

katharostech:gl-via-surfman-0.5-backportkatharostech/gfx:gl-via-surfman-0.5-backportCopy head branch name to clipboard