RFC: simple cli binary to hash pws and verify hashes

[ibotty]

I don't program in rust often, so please don't hesitate to say even basic things.

Still missing is the following.

• ability to specify hash specific parameters for hash
• a man page,
• bash autocompletion.

It uses clap and rpassword.

fixes #17..

[inejge]

Thanks for the PR and the accompanying issue, but I'm closing this for the reasons described in my reply to #17.