A very rough-cut XSL to generate an IIIF-Manifest compliant JSON file. Needs the interfaceConfig.xml file to be updated with document-iiif-manifest.xsl as a 'sa' argument; also currently relies on a common section of document.xsl to be carved out as document-core.xsl so it can also be used in document-iiiif-manifest.xsl (as inheritance/xsl-import was not the appropriate route to do this)