Support visual diff of schematic files as well.
Support visual diff of schematic files as well.

Limitations:
* Assumes all sheets to be the same size.
* default DPI settings makes quite large images.

Signed-off-by: Karl Palsson <cf2921c53fd940e0bab438c671bbd1b17f30b86b@tweak.net.au>

fxkr/eagle-diff,fxkr/eagle-diff