Make brotli and zstd optional again

[DerGuteMoritz]

Since it came up a few times now, I looked into making zstd and brotli optional again. Turns out there was a pretty easy workaround (see second commit). With this branch, the repro from #703 doesn't crash anymore.

[KingMob]

I wonder if we're just shifting around the set of people who will complain :)

Though truthfully, based on the number of downloads I see on Clojars, I don't think Aleph is used much anymore, so there probably won't be many complaints.

[DerGuteMoritz]

I wonder if we're just shifting around the set of people who will complain :)

True. I guess we could have another vote about it but given the meager turnout last time...

Though truthfully, based on the number of downloads I see on Clojars, I don't think Aleph is used much anymore, so there probably won't be many complaints.

Hmm indeed.... judging from these, at best there are maybe still 1000 users around? Perhaps it's time for a bit of a marketing campaign to re-ignite its popularity 😄

[KingMob]

Looks good. I think it's much safer to move this to Java.