Merge pull request #88 from Coeuvre/master

Fix bug that `mouse_move` event not working with GLFW back-end
Moved generic parameter to methods using `GameWindow`
Upgraded to latest Rust-Graphics
Moved code from 'TEMP-rust-png' into own library
Update README.md
Updated symlink info
Added presentation slides 'impl Game for App'
Removed opengles and added gl-rs support

Have testet this on windows with rust-snake, and it worked. Also the
file gl.es has been renamed to gl_back_end.rs.
Upgraded to lastest rust-graphics