Add loop and no-label options, possibly others

I needed to hide the "Image x of y" label and make images loop around, i.e. pressing next on the last image goes to the first image, and pressing previous on the first image goes to the last image. So I made the code.

But I also found this: http://www.justinbarkhuff.com/lab/lightbox_slideshow/#configurations
Which is a mod of an older version of LightBox2 with more options. You might consider adding these options too.

(sorry about the extra issue, new to github :-)