Use clap-rs Instead of ArgParser

Seems to me that there isn't a good reason that these utils don't use clap-rs. It would make them significantly more robust, and make them easier to implement and maintain. If there are any good reasons, please let me know. I'm willing to port things if we decide that it would be a good idea to use clap.

I realize that somebody put a lot of effort into writing the ArgParser crate, but it seems like the less code we have to maintain ourselves the better.