[#1433784] by dww: Major cleanup of revision 0e487b98.

- Renamed all functions that were operating on metadata to use "metadata"
  in their names, not "json".
- Moved all the logic for the metadata filename into a single function.
- Changed the command-line option to '--drupal-org-log-package-metadata'
  and if there's a value specified, we use that for the filename.
- Added extensive PHPDoc comments to all new functions.