`fzstd.compress` support

[SukkaW]

We want to use fzstd to better compress and decompress small piece of data with as high compression rate as possible.

Currently we are already using fflate, but we figure that zstd may achieve higher compression rate than deflate in our case.

[101arrowz]

This is not currently planned as my understanding of Zstandard is much worse than my understanding of DEFLATE, and in particular the compression heuristics that libzstd use remain rather arcane to me. However it's worth considering for a future update.