Fixed defaults for offset & spacing
Apply zoom & affine transforms when angle != 0

There was no reason to include the zoom, crop, and affine
transformations inside the 'angle != 0' condition.
Optionally soften borders by applying transparency

The parameter is called 'shadow' but it's a pretty crap shadow effect
because it's uniform all around the pages. For a true drop-shadow effect
you would need to take into consideration the angle of rotation, affine
transform, position of "light source" etc. We don't do any of that.