* [XML_TO_RDF,EXT] Allow optional properties to be specified in the propery filter. This means that these properies are parsed when they occur in the XML DOM (and are non-empty), and the clause does not fail when they are not in the XML DOM.
* [XSD_INTEGER,SC] The lexical mapping now uses the subrule of decimal parsing that applies to integers (i.e. the one without a decimal).
Merge branch 'master' of https://github.com/wouterbeek/PGC