Reexported `OpenGL` from shader_version

Closes https://github.com/PistonDevelopers/opengl_graphics/issues/99
Merge pull request #104 from bvssvni/master

Reexported `OpenGL` from shader_version
Fixed deprecated warnings for piston-image
Merge pull request #105 from bvssvni/master

Fixed deprecated warnings for piston-image
Added metadata to Cargo.toml, renamed package

* Upgraded to latest piston-image
* Updated project description in README
Merge pull request #106 from bvssvni/master

Added metadata to Cargo.toml, renamed package