Revamped the bindings

[exelotl]

Hi! I updated these bindings for the current version of SDL_gpu, and renamed all the functions and generally cleaned everything up. Hope this is useful! Let me know if there are any issues.

btw I'd gladly become a collaborator or just maintain my fork separately, whatever floats your boat. :)

[smokefilledrooms]

Thanks, great work!

I just put this up here because someone asked for them and don't have much interest in maintaining it, so honestly if you'd like to take over this repo or have me close and redirect to your fork (I'm new to github so I'm not quite sure what the options are) I'd be cool with whatever. I'm not sure if you're aware, but https://github.com/Vladar4/sdl2_nim has sdl-gpu bindings too now. It would probably still be good to have a separate set of bindings for users of the nim-lang SDL bindings (and nice for discoverability).

Anyways, let me know what you'd like me to do with this repo and I'd be happy to do it.

[exelotl]

Redirecting seems awkward so yeah just add me as a collaborator :)

Ah yeah, I did find out about the sdl2_nim repo just after making this PR. I'm really unsure what to do now, the official nim-lang/sdl2 bindings are kinda inconsistent compared to sdl2_nim which is cleaner and better documented. I was worried about name conflicts but it does somehow seem possible to have both installed at the same time without trouble.

I guess I should contribute some fixes to sdl2_nim and then advise people to use that instead? In an ideal world sdl2_nim could become the new nim-lang/sdl2 but I'm not sure that will happen :'(