Catch only ImportError when trying PIL imports
Make setup.py executable
Update the github url for the project
Implement a way to preserve the original image ratio

ImageWithThumbsField now accepts the preserve_ratio flag. If set to
True, generated thumbnails will respect the original image's ratio.
preserve_ratio is set to False by default for backwards compatibility
reasons.

Fixes issue #4. based on a patch by Gaurav Kumar.
Add myself to AUTHORS