WIP First semi-working version of export

This is hard-coded to only export a single catalog, and I haven't
yet validated the format of the output against the import format.

Next step is to write some tests that do that.
Basic export is working

Includes a test to validate against a real JSON catalog.  Needs
lots more tests, docs, polish.
Basic import/export functionality complete
WIP, working on docs and tests for import/export
WIP Added tests for two of the new catalog namespaces; passing