Add verify to nipap-passwd

Add new feature to nipap-passwd to verify if a username and password is correct. The tool will show if the user exists and if the password is correct.

For request https://github.com/SpriteLink/NIPAP/issues/467
Wow great, I am very happy to hear that! So you are saying that you are ok with the changed syntax in https://github.com/SpriteLink/NIPAP/pull/458 ? I am asking because on your comment https://github.com/SpriteLink/NIPAP/pull/458#issuecomment-33461320 you did not seem to be satisfied.

Currently the syntax in this patch here is as you posted and I also edited the man.rst file.