Base version (SDL 2.0.9) is outdated

[JayFoxRox]

We should rebase to the latest upstream.

The upstream of SDL2 is at 2.0.12 by now. However, the nxdk version is still stuck on 2.0.9.

Interesting changes for SDL2 are primarily in the input portion, which will allow querying the device per player index, and functions to query the device type (although original Xbox is not a supported style yet).

[JayFoxRox]

There were a bunch of performance improvements in SDL 2.0.10 format conversions in CPU blitting; so this is actually not just a feature upgrade, but could mean significant performance boosts for some applications.

See https://github.com/SDL-mirror/SDL/commits/626415306a6c8883f20e0c29fa1ed9f6e28a6259 and so on. Particularily on slow platforms with poor memory performance (like original Xbox) this should be significant.

[dracc]

I looked into a quick rebase; turns out our sdl_joystick code does not work with sdl 2.0.12 - It'll need a big overhaul/rewrite.

SDL joystick internals has changed so our code no longer compiles. Some of the backend structure has changed - it seems it's not just renaming so our code also needs a new structure.

[JayFoxRox]

It doesn't require much to make it compile. I also tried a rebase in JayFoxRox#4; I might work on it again once all remaining PRs on this repository have been merged and the rebase has been confirmed to work.

[JayFoxRox]

Upstream already on 2.0.22 now.

Since #40 the development speed of SDL seems to be even faster. Most of it in the renderer, but there are some GameController changes which might be useful, too.
Also probably good to remain in sync to avoid larger rebase conflicts in the future.

[sharkwouter]

It would probably be best to upstream the port. In my experience the SDL people have been very open to accepting code for homebrew SDKs within their codebase. The Vita, PSP and most recently the Nokia N-Gage ports have all been upstreamed.