fixed cropping images wide images

I had to rewrite some of the crop function to get cropping working on wide images. It works for tall images as well. I haven't tested how specifying the $top/$left... would affect this as I don't have any acceptance tests in mind for that. Do you want to give this a whirl? As an added bonus this code with automatically centre the crop, trimming off even amounts from the left/right or top/bottom as required by the scenario.

This is related the the issue #7 I opened.

https://github.com/dbashyal/Magento-resize-category-images/issues/7