Binding: if FLAG_BIND_INSERT_XML is not set, allow null XML data
rFont processing: work in progress
XHTMLImporter is an interface (implemented in docx4j-ImportXHTML project)
Support using a customised WriterRegistry
- Use XHTMLImporter interface
- OpenDoPE: Take Word styles into account in importing XHTML

SDP: store CSS for re-use
Merge remote-tracking branch 'origin/master'