Automatic apidocs

Closes #34 

This now automatically serves all resources in the resourceListing at /api-docs with no user-side configuration required.

More refactoring is included since mental taxation was reaching peak levels with existing code. You might find walking through the commits more helpful than the final diff.

Confirmed that the final product does what we want by hooking it up to a sample pyramid application and it works with Swagger-UI nicely.
I think it might be helpful if you could document the type for schema_resolvers?