De-lint test suite.

Change-Id: Ib0b4471052688ff220a7f331abcb27e20a410bb7
Tweak metabook.json to better match spec.

Put the 'type' field at the top of each object; add 'type' field to
FileRepo objects.

Change-Id: I7462c80d7456051578b1b4e69ed1a7aeda55abd8
Add CLI option to force a toc.

Change-Id: I59a0baee226a0df90989112b69744c843cf7e5ff
Factor out promise utility module 'P', shared with mw-latexer.

Change-Id: Ida24d906a37afa557b9b093f91e4ef038b37d6f1
Ensure spidered filenames are unique.

This avoids filename conflicts in multiwiki collections.

Change-Id: Ideb3260486623bcae2f9aaffd957d40cf4e49a98