Merge pull request #88 from bvssvni/master

Upgraded
Updated submodules
Merge pull request #89 from leonkunert/master

Updated submodules
Updated gl-rs
Merge pull request #90 from leonkunert/master

Updated gl-rs
Upgraded, deleting symlinks on build

Closes https://github.com/PistonDevelopers/piston-workspace/issues/93
Closes https://github.com/PistonDevelopers/piston-workspace/issues/94