Allow Section title to be optional.
Expand importer's range of known elements.

Include XML elements when fetching text content, not just text,
and error on unknown hierarchy elements.
Construct title from any num/heading/subheading elements present.

Optional, so don't mind if they're absent.
Add date handling in speeches and in preface.
Utilise by attributes and TLCPerson meta headers on import.
Handle ZA's slightly different current AN use.