data: Add access to route metadata in the templating data. It's available under `route`. Also, rename `slug` to `rel_url`, because it's confusing when `slug` could be the route metadata of the same name as provided by the default page source. The old `slug` is still there for backwards compatibility though.

from piecrust.serving.server import WsgiServer


def get_app(root_dir, cache_key='prod', enable_debug_info=False):
    app = WsgiServer(root_dir,
                     cache_key=cache_key,
                     enable_debug_info=enable_debug_info)
    return app