Feature Request: Specify compression command/parameters

[code8buster]

This is low priority, maybe it is interesting to have some customize ability with compression?
For instance, maybe you don't want almost uncompressed zstd level 1 but are too impatient for the max, or maybe you want to compress even higher than what xz --max allows.

I'd like it to be somewhere in the middle, around zstd 8, but being able to change it based on my mood would be very nice.

Thanks for your responsiveness to other issues Piero