Usage example:

    $app->register(new UrlGeneratorExtension());

    $app->get('/hello/:name', function($name) {
        return "Hello $name!";
    })
    ->bind('hello');

    $app->get('/go', function() use ($app) {
        $url = $app['url_generator']->generate('hello', array('name' => 'Fabien'));
        return $app->redirect($url);
    });

Thanks to @choffmeister.