video and default width/height support

[gabesmed]

Hi Jbutz. Thanks for the great library - this is exactly what I need for a project. I was using this for HTML5 video and found I needed to extend it to get the video size. Here's the extension -- feel free to incorporate if you'd like!

[archonic]

I found a similar plugin that has support for videos with width and height: http://ashleydw.github.io/lightbox/