cups-airprint-1.1-bp156.3.1

- python3.patch: Port script to python3
- pdf-support.patch: Fix printer discovery
- Add minimal build check to verify the script can run at all

- Inserted a new section "2. CAVEATS" in README.SUSE
  about possible limitations of AirPrint support via CUPS.

- Requires cups-filters >= 1.0.25 and cups >= 1.6:
  At least some iOS apps send the URF format when printing via
  AirPrint so that the matching urftopdf filter that is provided
  in cups-filters >= 1.0.25 is required to convert URF into PDF
  (the nowadays standard printing data format which can be further
  converted into the printer's native data format).
  Because cups-filters cannot be reasonably well used with
  traditional CUPS <= 1.5.4 also a modern CUPS >= 1.6 is
  in practice required.

- Changes due to review feedback
  * Drop CUPS as build requirement
  * State required CUPS version at runtime
  * Document why CUPS-internal DNS-SD is insufficient
  * Many minor documentation improvements

- Initial version.