Share link with autosave

[curiousdannii]

It would be nice for testing purposes, and probably for more than just that, to be able to share a link to a particular point with an autosave/save game.

So that URLs aren't insanely long, engines would have to send xored memory (or just quetzal style savefiles.) We should look at the GlkApi autosave to see if there's anything there to trim. And then use some kind of compression (brotli? zstandard? something else?), before finally base64 encoding it.