public function avatar($options = [])
    {
        $options = (array)$options;
        $options += [
            's' => 80,
            'd' => 'mm',
            'r' => 'g'
        ];

        $url = 'http://www.gravatar.com/avatar/';
        $url .= md5(strtolower(trim($this->get('email'))));
        $url .= "?s={$options['s']}&d={$options['d']}&r={$options['r']}";

        return $url;
    }