add XSD 1.1 support

[pahjbo]

Could add support for some XSD 1.1 features to the generated XML schema

This snippet shows how to get the validation bootstrapped in Java

 System.setProperty("javax.xml.validation.SchemaFactory:http://www.w3.org/XML/XMLSchema/v1.1",
                "org.apache.xerces.jaxp.validation.XMLSchema11Factory");
 
            new org.apache.xerces.jaxp.validation.XMLSchema11Factory();
            SchemaFactory sf = SchemaFactory.newInstance("http://www.w3.org/XML/XMLSchema/v1.1");