title: symfony twig extension get config variable
body: <p>I'm trying to get config variable from custom twig extension.</p>
  
  <p>how can I get someVar from config ?</p>
  
  <pre><code>// src/AppBundle/Twig/AppExtension.php
  namespace AppBundle\Twig;
  
  class AppExtension extends \Twig_Extension
  {
      public function getFilters()
      {
          return array(
              new \Twig_SimpleFilter('price', array($this, 'priceFilter')),
          );
      }
  
      public function priceFilter($number, $decimals = 0, $decPoint = '.', $thousandsSep = ',')
      {
          $price = number_format($number, $decimals, $decPoint, $thousandsSep);
          // HOW TO ACCESS TO CONFIG VARIABLE
          $price = '$'.$price;
          return $price;
      }
  
      public function getName()
      {
          return 'app_extension';
      }
  }
  </code></pre>
  
  <hr>
  
  <pre><code># app/config/services.yml
  services:
      app.twig_extension:
          class: AppBundle\Twig\AppExtension
          public: false
          tags:
              - { name: twig.extension }
  </code></pre>
  
  <hr>
  
  <pre><code>twig:
      debug:            "%kernel.debug%"
      strict_variables: "%kernel.debug%"
      globals:
          someVar: "someValue"
  </code></pre>