Add support for Zstandard compression

[sabi0]

Zstandard provides much better compression (and speed!) than gzip (uncompressed: 5580 MB, gzip: 1517 MB, zstd: 717 MB).
It would be great if GoReplay was able to read the input from zstd compressed files.
Compressing output with zstd would be nice too, of course.

P.S. Unfortunately gor does not seem to support reading the input from stdin either. So one cannot do zstd -d recording.gor.zst | gor ....