Add support for more features of the Wikipedia REST API

[tomayac]

Add all applicabale functions from https://en.wikipedia.org/api/rest_v1/#/.

[tgr]

Article extracts / summaries (/page/summary/{title}) would be quote useful - it's like Wikidata descriptions but longer and better curated. Everything else, I don't think so. Maybe /page/related/{title} (a kind of search for articles with similar words) if I squint hard enough?

[tomayac]

I'm happy to accept and review PRs that add new functionality, but don't have the capacity at the moment to work on this myself.