Return the resources from an API implementation module.

    The results returned here are used to generate documentation.  They aren't
    currently used for anything in production.

def extract_resources(api_module):
    """Return the resources from an API implementation module.

    The results returned here are used to generate documentation.  They aren't
    currently used for anything in production.
    """
    endpoints = extract_endpoints(api_module)
    resource_classes = [ e._returns.__class__ for e in endpoints ]

    return list(set(resource_classes))