Add and export 'get-item-type
Augment 'query to accept optional parameters.

Also expand its documentation slightly, to make the API clearer.
Include comments when updating narrative items

Extend 'add-narrative-version and 'create-narrative-item to accept an
optional 'comment argument, and to pass that through.
'get-narrative-version-listing retrieves comments

If a comment was recorded along with a narrative version,
'get-narrative-version-listing now retrieves that as well as the
version's UUID and datestamp.
Expand 'add-narrative-version test with comments

Update the test suite to check whether 'add-narrative-version responds
well when handed a comment as well as text content.