SDL3 examples: Full game and app demos

I've been messing with SDL3 and LuaJIT for a while, and I think it's a qualitative improvement over SDL2. People should also check out the test folder in the repo[0] for more interesting stuff and of course the Discourse forum[1].

[0]https://github.com/libsdl-org/SDL/tree/main/test

[1]https://discourse.libsdl.org/

SDL is cool!!!