== How to use

For a given model, will generate a new model to hold an image, 
and will create a "service" class that allows the original 
model and its image to be updated in the same transaction.

== Usage

script/generate attachment_fu_image class_that_needs_image

== Example

For example, if you have a User model, and want your users to have
images, then run

script/generate attachment_fu_image User

This will generate a new model, UserImage, and will also generate
the UserImageService.  The service's constructor takes a User and 
a UserImage.  Calling save on the service saves both the model
and the image model.

If the image is nil, the image is not modified.