new xISBN API - beta

I have been working on a new xISBN service in last few months, and I had a chance of sharing latest progress in excellent code4lib conference held in Athens, Ga. Thanks for all your valuable comments, folks!

The new service is now running as a beta version. We add more features/metadata, at the same time try to keep the API simple and clean.

x-identifier list is a venue for comments/suggestions.