Create `routes` type

[Archmonger]

This function needs to match the react-router equivalent.

See #2 for more details.

[rmorshea]

This is referred to as a router presently. Can rename though.

[Archmonger]

routes and route are two different callables in react-router.

Our router seems to be equivalent to with BrowserRouter, which is the root routing node

[Archmonger]

Closing due to this admonition on the react router docs

If you're using a data router like createBrowserRouter it is uncommon to use this component as routes defined as part of a descendant tree cannot leverage the Data APIs available to RouterProvider apps.