Added option to set index of image to display first

[bjarneg]

I'm new to this github thing, so sorry if I'm doing things wrong. But, like your plugin it's fast and simple. I missed an option though, to set the first image to display so I added that.

I guess I've just could have skipped the

pic.attr("src", $(this).attr("src"))

line, and loaded the images in another way, but I choose the slightly easier way for now.

[matdumsa]

Thanks Bjarne, I'll look at the code over the week-end and merge it into master