public static function percentage($number, $options = array()) {
        if (!is_array($options)) {
            $options = array('places' => $options);
        }

        $options = $options + array(
            'thousands' => ',',
            'decimals' => '.',
            'places' => 2
        );

        return number_format(static::precision($number, $options['places']), $options['places'], $options['decimals'], $options['thousands']) . '%';
    }