$twig->addFilter(new TwigFilter('htmlentities', 'htmlentities'));
$twig->addFilter(new TwigFilter('md5', 'md5'));
$twig->addFilter(new TwigFilter('format_date', array($app, 'formatDate')));
$twig->addFilter(new TwigFilter('format_size', array($app, 'formatSize')));
$twig->addFunction(new TwigFunction('avatar', array($app, 'getAvatar')));