Usability: runtime docs

[zverok]

It's not hard to generate some more code, and allow to have things like:

client.query.params
# => [:titles, :list, :meta, :generator....]
puts client.query.help
# Prints something like this page: https://en.wikipedia.org/w/api.php?action=help&modules=query

With multitude of actions and modules and modules and submodules... Can be REALLY helpful.