fuse Merge Request #31: SDL 1.2 to SDL 2.0 migration (open)

I have made the changes to remove SDL 1.2 dependency, and have SDL2 dependency only.
Key takeaways:
* removed "unicode" stuff - SDL2 is unicode by definition
* removed Meta_X and Super_X buttons - SDL2 does not have these definitions
* removed "fullscreen mode change" - if we want fullscreen - we should be utilizing current resolution (if user wants another resolution - it's their business to accommodate to that, before running the "game")
* use SDL2 texture/renderer natively
* use SDL_PIXELFORMAT_RGB565 only - let SDL/renderer handle the conversions

Tested on RPi4 & RPi5 - works fine with both X11 & wayland.

Potential issues:
* full screen mode is not completely perfect yet - need to do some work on switching
* temporarily disabled rectangle updates - refresh the whole canvas (to test the performance "in the worst case")
* mouse grab - need to make sure kempston mouse works fine (I test Pentagon512/gluk)

Let me know if you have any questions, suggestions or comments. Thanks for the review! Looking forward to work it out to the finish line and merge it.