Merge pull request #394 from bvssvni/master

Removed PortAudio code
Merge pull request #395 from bvssvni/master

Removed audio code
Merge pull request #397 from bvssvni/master

Added conditional compilation for GLFW and SDL2
Merge pull request #398 from bvssvni/master

Upgraded to latest Rust-Empty
Merge pull request #399 from bvssvni/master

Removed Rust-Graphics
Merge pull request #401 from bvssvni/master

Updated examples
Merge pull request #403 from bvssvni/master

Removed `Context` from `render` method
Added `GameIteratorSettings` argument to `Game::run`

Closes https://github.com/PistonDevelopers/piston/issues/323