adds zet

[yarrow]

Self-nomination. I thought about putting zet into the Unix-to-Rust table as a near replacement for uniq and comm, but its 161 stars compared to the myriad stars of many others makes that seem a little brash, and zet doesn't yet support case-insensitive comparisons.

[sts10]

Thanks! Yeah, I think I need to start restricting the table to closer replacements.

[yarrow]

Thank you!