Module for creating a ring router (a function that receives a ring
requests and dispatches to a handler function based on the request's
URL). It ties together the sugar for defining reitit routes and
liberator handlers.

The module uses routes produced by
`sweet-tooth.endpoint.routes.reitit/expand-routes`. These routes
contain metadata that allow the module to look up vars that define
liberator handlers. The module is responsible for associating routes
with handlers.

The module is also responsible for adding each handler's
configuration to the system's integrant configuration, reducing
boilerplate for the developer.

We derive handler keys from `::handler`. We then define
`ig/init-key` methods for those keywords, where the method returns a
handler function.

This module serves Sweet Tooth's goal of reducing the boilerplate
required to get a system running, reducing the potential for errors
and allowing the developer to focus on what's unique to their
application.