[PATCH 1/2] ui-snapshot: add support for zstd compression

[Jason A. Donenfeld]

Wow, thanks for doing this. I had just been discussing this with
Unit193, who submitted a similar but not as complete patch a few days
ago to me on IRC.

We had been discussing which compression level to pass to zstd or to
leave it as default. I think Unit193 had some thoughts on that, so
CC'ing him in case he wants to jump in.

Barring any change as a result of that, happy to merge this.

Thanks.