Subclasses of `ActionController::Metal` are stripped-down controllers.
We want to recognise them as ActionController controllers.
There are some common ActionController methods that are not available in
Metal, but these are not likely to be used anyway as they would throw an
exception, so I don't think there's much harm in including them in the
modelling.
Add `Route` classes which model Rails routing information, typically
defined in a `routes.rb` file. We extract only the most basic
information: HTTP method, path, controller and action. This is enough to
determine whether a given controller method is a route handler, and what
HTTP method it handles, which is useful for, among other things, the URL
redirect query.
