Merge pull request #40 from bvssvni/master

Fixed missing docs warning
Added link to how to contribute

See PistonDevelopers/piston#715
Fixed namespace issues with lates nightly.
Merge pull request #42 from leonkunert/master

Fixed namespace issues with latest nightly.
added OpenGL 4.5 support
Merge pull request #43 from DaemonLee/master

added OpenGL 4.5 support
Reexported `OpenGL` at top level

Closes https://github.com/PistonDevelopers/shader_version/issues/44