TODO: Provide IO layer to support SDL agnostic (or any rendering / input framework) version

[MikeDX]

Currently the emulator utilises SDL exclusively, but with some minor changes, this can be much more open.

I currently have code to support SDL1.2/2 in a test branch locally, which renders the screen to a buffer and accepts keycodes as an array (like the existing keymap matrix). This should allow any future port to use whatever rendering they like, such as framebuffer, GDI, openGL, outputting to RGB leds... etc.