Merge pull request #44 from bvssvni/master

Upgraded to latest gfx-rs
Add SDL2 and SDL2 mixer to make travis happy
Add travis CI status to readme
Merge pull request #45 from lucidd/master

Make travis happy
Removed gfx_cube and gfx_triangle

Closes https://github.com/PistonDevelopers/piston-examples/issues/46