Initial commit: basic skeleton.
Add some sample bundles.
Finish refactoring the existing spider.
Create images/ directory in appropriate format; create zipped bundle.
Add revision IDs to metabook.json; write metabook and nfo.json to bundle.
Dump parsoid output to an sqlite3 db.
Refactor to use promises to manage asynchronous callbacks.
Generate siteinfo.json file in the bundle.
Factor out common API request code.
Add html.db to bundle.
Minor bugfixes: honor revid in parsoid fetch; handle nfo.json input.

nfo.json has a field named base_url, which is equivalent to the field
named baseurl in metabook.json.  Convert between them.
Begin implementing the revisions-1.txt bundle file.
Refactor to use 'wiki index' instead of 'prefix' for article titles.

The upstream bundle format uses an array of wiki information when
books span multiple wikis.  Use this consistently in the item format
to allow bundling articles which span wikis.
Use correct file names in images/ directory.
Add revisions for image description pages.
Accomodate parsoid: use 'enwiki' prefix, not 'en'.
Fetch image size metadata.
Limit maximum resolution of downloaded images.
Don't download audio files.
Better handle --prefix on the command line.

Refactored CLI interface to use promises, so that we can do an async
query for prefix information.  This removes a few more hacks that depend
on wikimedia-style API URLs.