Shortcode bug

Hi, thanks for a great plugin.

There is a typo in shortcode handling:
http://plugins.trac.ww.wp.xz.cn/browser/wp-slider/trunk/wp-slider.php#L331

Also, i didnt found shortcode documented anywhere. (the best place should be beside the generated php code in administration)

http://ww.wp.xz.cn/extend/plugins/wp-slider/