public function addEvent($start, $end, $summary = '', $description = '', $url = '', $uid = '')
    {
        if (empty($uid)) {
            $uid = md5(uniqid(mt_rand(), true)) . '@EasyPeasyICS';
        }
        $event = array(
            'start' => gmdate('Ymd', $start) . 'T' . gmdate('His', $start) . 'Z',
            'end' => gmdate('Ymd', $end) . 'T' . gmdate('His', $end) . 'Z',
            'summary' => $summary,
            'description' => $description,
            'url' => $url,
            'uid' => $uid
        );
        $this->events[] = $event;
        return $event;
    }