Add max width and height option

[jhnvz]

Lightbox looks to big for images with a larger size then screen. I've added a max width and height option so you can adjust max width and height. I've set the defaults to 800x600 but you can override them by setting the option(s) to false or null.

[lokesh]

Thanks for the PR, unfortunately there was not enough interest in this feature to have it be brought into master.

[lokesh]

I stand corrected. I found a couple of requests for this feature.

I'll move this into master and queue up for release. Thanks.

[jhnvz]

Thanks! I already forgot about this PR ;)