Prepare release 1.2.0

State file update, Makefile

- Use standard journalctl "cache-file" mechanism
- Introduce "install" target in Makefile
- Update README

Fix^2: disregard stderr also on exit 1

Fix: ignore stderr *only* on exit 0

Release 1.0.3

Fix error in options handling

Release 1.0.1

Ignore -v for compatibility.

Document possibility of specifying an URL for the rules file.