Added how to compile with OpenGL back-end

Closes https://github.com/PistonDevelopers/rust-graphics/issues/528
Merge pull request #541 from bvssvni/master

Replaced `Stroke`, `Fill`, `Clear` with `Draw`
Merge pull request #542 from bvssvni/master

Updated to latest Rust-Empty
Merge pull request #543 from bvssvni/master

Added 'build.sh' and latest Rust-Empty
Added initial Cargo config file
Merge pull request #544 from TyOverby/cargo-initial

Added initial Cargo config file
Upgraded to latest Rust-Empty