Support SDL2/SDL2_image on all platforms
CMake currently doesn't come with the modules to support SDL2, only SDL. SDL2 has been out for years, and is relatively easy to support. There's a version of the SDL module changed to work with SDL2 here that the author gave me permission over email to submit as a pull request. If CMake is willing to take it I will submit said pull request, if not please close this ticket and I won't put in the time. Thanks, -Pat