http://www.xeekworx.com/sdl2guides/11-sdl2guides-02
https://wiki.libsdl.org/CategoryAPI
https://wiki.libsdl.org/MigrationGuide
http://www.willusher.io/sdl2%20tutorials/2013/08/17/lesson-2-dont-put-everything-in-main
http://lazyfoo.net/tutorials/SDL/18_key_states/index.php