Usage:

$app = new Application();
$app->register(new TwigExtension(), array(
    'twig.path'    => __DIR__.'/../templates',
    'twig.options' => array('cache' => __DIR__.'/../cache', 'debug' => true),
));

The "app" variable is registered as a global variable, so it is accessible in all templates:

$app['routing'] = new UrlGenerator(...);

{{ app.routing.generate('homepage') }}