If we follow your suggestion from #47 then the current naming of the method makes sense. 

So I think the operation here is to create an `Authenticator` whether it will be stored in the cache or not. The update method will be called in the `Silhouette` trait to update an already exiting `Authenticator`. Update doesn't mean that it will be updated in the backing store, it means that the `Authenticator` gets updated. e.g. set a timeout. If you think about the client side session authenticator, then this authenticator gets never be persisted. So I see no use for a save method.