SDL2 proof of concept (no input / Ruby support)

Conflicts:
	examples/Tutorial/Tutorial.xcodeproj/project.pbxproj
SDL Input
Working cross-platform multi-gamepad support thanks to SDL2
Comments
(Untested) setMousePosition and initial SDL TextInput implementation
Prevent main loop from busy-looping when window is obscured (=no vsync)
Clean up Input.hpp
Finish SDL TextInput implementation
Fix mouse button mapping
SDL-based idToChar and charToId, formatting
Remove TransformProcessType() call from Window.cpp, SDL already does this <3
Implement Gosu::screenWidth(), screenHeight() using SDL
Move Transform into GraphicsBase.hpp
Preserve aspect ratio in fullscreen mode
Some fixes for windowed mode
scheduleGL is not experimental by any means
Shrink window if necessary
Keep Gosu::Song playing
Make sure Graphics and Input agree about letterboxing
Use C++03, C++11 doesn't buy us much here