bind<T extends Object> static method
turn the route param param into a value before the controller
runs. resolve gets the raw text and gives the value, or null
when there is none: then the request gets 404.
read it with req.bound<T>(param), or add a controller parameter
of type T. call it before the server starts.
Route.bind<User>('user', (String id) => User().find(id));
Route.get('users/{user}', (DoxRequest req, User user) => user);
Implementation
static void bind<T extends Object>(String param, RouteBinder<T> resolve) {
_bindings[param] = RouteBinding(T.toString(), resolve);
}