destinations.ml: add a compressed_file_destination that uses zstandard

[Lilydemi]

Trace files can be large and hard to share. Using zstd to compress trace files allows users to decrease their file sizes, as demonstrated here:

$ du -sh trace.fxt trace.fxt.zst
472K    trace.fxt
56K     trace.fxt.zst

This is a preliminary attempt at adding a compressed file destination. We have some open questions that we want to raise in the PR.

One thing we had to do is we had to make an original_filename labeled argument. This is because, sometimes, magic-trace uses /proc/self/fd/$FD paths as a way to prevent a race condition when serving traces.

[hlian]

This addresses #154 (just to link the two)

[hlian]

@Xyene ready for rereview if you have free time!