XSD 1.1 support

[dalcorta]

The plugin doesn't support XSD 1.1. I have a schema with the xs:override tag. When I execute the plugin the following error appears
org.xml.sax.SAXParseException: s4s-elt-invalid-content.1: The content of 'schema' is invalid. Element 'override' is invalid, misplaced, or occurs too often.