[UrlGeneratorExtension] service for generating URLs for routes

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.

src/Silex/Extension/UrlGeneratorExtension.php

+<?php
+
+/*
+ * This file is part of the Silex framework.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Silex\Extension;
+
+use Silex\Application;
+use Silex\ExtensionInterface;
+
+use Symfony\Component\Routing\Generator\UrlGenerator;
+
+class UrlGeneratorExtension implements ExtensionInterface
+{
+    public function register(Application $app)
+    {
+        $app['url_generator'] = $app->share(function() use ($app) {
+            $app->flush();
+            return new UrlGenerator($app['routes'], array(
+                'base_url'  => $app['request']->getBaseUrl(),
+                'method'    => $app['request']->getMethod(),
+                'host'      => $app['request']->getHost(),
+                'port'      => $app['request']->getPort(),
+                'is_secure' => $app['request']->isSecure(),
+            ));
+        });
+    }
+}