Changes to better support possible outputs of the Connector Framework.

Changes to better support possible outputs of the Connector Framework.

* New, trivial, templates to handle thirteen additional elements:
  available, citation, relevance, booktitle, copyright,
  copyrightabstract, pubtype, doctype, extent, format,
  languageitem, languageabstract and permalink.

* Comment on how the "medium" field is ignored in favour of an XSLT
  parameter.

* Comment on the "holding" element which seems to be a synony, of the
  "item" container.

We now have *a lot* of near-identical tiny templates for handling
individual fields, each mapping the CF's data
	<NAME>VALUE</NAME>
to PazPar2's equivalent
	<pz:metadata type="NAME">VALUE</pz:metadata>
Should these all be replaced be a single general-puspose rule?  That
would also mean that we'd no longer need to update this stylesheet
each time parseTask.cff changes.