It would be nice if there was an option to reference entities by key_name or by
numeric ID, rather than key.
Keys are convenient for developers because they're unique and fast. But they're
also long, which means they don't make the friendliest URLs.
It would be nice if I could tell appengine-rest-server what type of identifier
to use when constructing (and interpreting) URLs. Perhaps this could be done as
an additional parameter for Dispatcher.add_models, so this could be set on a
per-model basis?