Allow cropping image to a specified width and height.

Hi,

I added a new feature to be able to crop an image, if dimensions of the target image are not equal to the one from the original image. That means, if your original image is say 100x200px and your target image is 50x50px, you really get a 50x50px image instead of a 25x50px image.

I also changed dependencies from PIL to Pillow, which is much better maintained.

I also added a buildout.cfg and bootstrap.py to be able to run tests in a buildout supported environment.