Port to clap-rs
I did a number of things here: the *add, *mod, and *del utilities, as well as id recieved substantial changes, probably what you'd call a rewrite. This was of course using clap-rs. These should all be very stable at this point (except unimplemented features in usermod, grr) getty, passwd, and su are simply ported, using clap for arg parsing. I didn't change any of the logic, just swapped ArgParser for clap. Fixed a bug with passwd and unset passwords I'll open issues about the ones I didn't mention.
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