replace original xsd2json with node-xsd2json for PR

Hello,

First of all: I absolutely don't expect you to accept this PR as it is.

It contains a whole new node.js CLI program that wraps around your original prolog program in an attempt to fix the limitations I encountered. You can have a look at the readme for instructions on how to test it.

Most of it you will probably consider dirty workarounds, but I am quite in a hurry to validate the feasibility of XSD->JSON schema for my company. And I need support both for inclusions and type extensions. I will be glad if my code shrinks when your program makes progress.

Of particular interest for you: the test directory contains a small set of XSDs with a good overview of inclusions and extensions test cases.

Thanks