[2.0.0-prerelease] SDL 3.1.3 support

BindBC-SDL 2.0.0 Pre-Release 1

Here's the first preview of bindings to SDL3. Please test it at your leisure and report any issues you may encounter.

What not to expect

API compatibility

This release will NOT be fully API-compatible with BindBC-SDL 2.0.0 or future pre-releases. SDL3 is has only reached stable a ABI—not stable API. Also note that in the long-run this release tag might be invalidated by commit-squashing in order to preserve a smaller git repository size, so do not rely on this tag existing indefinitely. If you are working on a project, feel free to migrate now but be prepared to change some of your code later.

SDL_image, _mixer, etc.

None of the 'satellite' libraries have 3.0 previews available as of yet, so currently they are just dummied out until I can be sure of how to update their bindings. Sorry about that.

What's next

The moment I was done with this release SDL 3.1.6 came out, so that's what I'll be working on next. It is not API-compatible, so there will be some API breaking changes in v2.0.0-prerelease.2. This is the danger with using unreleased software!