Feature/sha512

This is a request for feedback, not yet a fully ready pull request.

It adds a nodejs cli mode to get the password (prototype only for now) and updates the code to prepare for using sha512 instead of sha1 (as its much harder to crack, some numbers in http://arstechnica.com/security/2013/05/how-crackers-make-minced-meat-out-of-your-passwords/).

If you aggree with the general direction I will continue and add a option to select the cypher and use sha1 only for backport compat.