Added new option (minHeight) to have a different height to width

Hi there,

We had a requirement for the box height to be different to the box width so I have made some changes (new option of 'minHeight') and while it seems to be working (IE8+, Chrome, Firefox) with 'resizeToFit: false' I would love some feedback and help to get it working with 'resizeToFit: true' if possible (or maybe this defeats the purpose?).

Thanks!