/some/route?color=red&color=green&color=blue.Navigator.pop via use of a Future.BREAKING: In order to support function handlers you will need to change all of your route
handler definitions to use the new Handler class. The RouteHandler definition has now been
removed.
Swapping out the handlers should be as simple as changing:
RouteHandler usersHandler = (Map<String, String> params) {}
to
var usersHandler = new Handler(handlerFunc: (BuildContext context, Map<String, dynamic> params) {});