Add the ability to get the Wikidata IDs for multiple Wikipedia articles

Currently `wd id` can only look up a Wikidata ID for a single Wikipedia page. It would be useful to be able to look up multiple IDs, whether through a `--batch` option to `wd id`, or via some other mechanism.

If added to `wd id` there would presumably also need to be a way to get the results as JSON, so as to connect the inputs and outputs.