More HTTP verbs, use plain node http server

* Support the standard HTTP verbs

* Use plain HTTP instead of express for performance. In the simple 'hello
  world' benchmark (ab -n10000 -c 10
  'http://localhost:8888/v1/enwiki/pages/foo/rev/latest/html') express yielded
  around 5200 req/s, while plain node was good for 9200 req/s

  We already implement our own routing, and plugging in middleware selectively
  is fairly straightforward & does not require using express itself. Express 4
  moved to direct use of third-party libraries anyway, so it's not even
  significantly more verbose.