Merge pull request #67 from bvssvni/master

Added Travis build button
Merge pull request #68 from bvssvni/master

Updated
Merge pull request #70 from bvssvni/master

Added link to SDL2 building information in README
Updated Submodules
Merge pull request #71 from leonkunert/master

Updated Submodules
Updated to latest Piston
Merge pull request #72 from leonkunert/master

Updated to latest Piston
Updated Piston
Merge pull request #73 from leonkunert/master

Updated Piston
Updated rust-image
Added rust-sdl2_ttf as dependency