title: Trying to get this Twig (Symfony2) function extension to register
body: <p>I'm getting an error:
  "twig extension FatalErrorException: Error: Class Acme\Bundle\MyBundle\Twig not found in app/cache/dev/appDevDebugProjectContainer.php"</p>
  
  <p>I've cleared the cache but this does nothing.</p>
  
  <p>I'm just trying to test setting it up and then I can put in all my logic.</p>
  
  <p>--</p>
  
  <p>A file named MyTwigExtensions.php</p>
  
  <pre><code>namespace Acme\Bundle\MyBundle\Twig;
  
  class MyTwigExtensions extends \Twig_Extension
  {
  
      public function getFunctions() {    
          return array(
              new Twig_SimpleFunction('link', 'generate_link')
          );
      }
  
      public function generate_link($params) {
  
          return "THE-LINK-HERE";
  
      }
  
      public function getName() {
  
          return "link";
  
      }
  
  }
  </code></pre>
  
  <p>In services.yml</p>
  
  <pre><code>services:
    my_extension.twig.extension:
      class: Acme\Bundle\MyBundle\Twig
      arguments: []
      tags:
        - { name: twig.extension }
  </code></pre>