Update TimberComment.php to have an avatar method

Is this helpful? I like how there are a bunch of easy ways i could do this.  

alternatives:

i could just swap out the class in my themes twig functions & then in single.twig do:
{% for cmt in post.get_comments(0, 'wp', 'comment', 'approve',  'KindlingComment') %}

    class KindlingComment extends TimberComment {
     function avatar($size='32', $default='<path_to_url>'){
          // Fetches the Gravatar
          // use it like this
          // {{comment.avatar(36,template_uri~"/img/dude.jpg")}}
          return get_avatar($this,$size,$default );      
        }
    }


or make a function in my theme twig.  yeah probably this one.

    $function = new Twig_SimpleFunction('avatar', function ($comment, $size = 32, $default = '') {
        return get_avatar($comment, $size, $default);
    });
    $twig->addFunction($function);