Add support for different aspect ratios

This patch adds support for different aspect ratios of thumbnail and
full-size image. The script now adapts automatically to the ratio of the
full-size image.
Add minified version of the patch and point to it in index.html
Using the reserved keyword class without quotes causes crash/error

Although IE8 does not support transforms, using the keyword class
without quotes crashes the whole javascript execution when using IE8
(other versions might be affected as well). Using quotes fixes this
issue.
Fixed typos, increased size of the example image (viewport testing)

Fixed typos, increased size of the example image (viewport testing).
Thanks to @andreasd for typo finding
Merge pull request #77 from maxee/master

Add support for different aspect ratios/Fix crash caused by using reserved keyword class without quotes