@starsirius => Render model references from API + more docs.

The meat of this PR is in the pages_controller which can now:

* Render JSON resources as examples from the API with things like `#{resource://artist/id=4d8b92b34eb68a1b2c0003f4}`.
* Render model field documentation directly from the machine description of the API with things like `#{modelref://Artist}`.

It's debatable. I wanted to have the artwork ID in there explicitly for now.