Simple raw input implementation

[dykebeard]

Yeah, the Sleep() is sketchy for sure. It's probably the right thing to just get rid of it, but I think a tiny one would be alright. Maybe just Sleeping if the window is minimized / not in focus would be smarter.

I'm not sure if WM_INPUT will be noticeably better off than WM_KEYDOWN performance wise, but we can also probably grab data for a controller in the future. I'm not sure how compatibility with different controllers will be, but everything could get potentially handled in one spot. It should be better off than GetAsyncKeyState() though, as it was probably possible to miss input.