Added support for SuperCard Pro .scp flux format

SCP file format details:
  http://www.cbmstuff.com/downloads/scp_image_specs.txt

Sample SCP disk image of Amiga Workbench 1.3 disk (non-blind, 2 revolutions):
  https://dl.dropboxusercontent.com/u/2553707/wb13.scp.bz2

Additional sample disk images are available upon request.