A simple SDL2 game framework.

1. TextureManager use SDL_Image to load image resources.
2. SDLGameObject handle all shown objects' draw/update/clean.
3. Player & Enemy all sub-classes of SDLGameObject.
4. Game class use a vector to manager all SDLGameObjects.
Game coder does not like std::vector? Whatever, maybe change
this someday when std should be abandoned.
5. main handles game loop with a fixed frame rate.
1080p/60fps, yes!!!!