Merge Debian packaging for release “1.5+dfsg.1-3”.

Merge Debian packaging for release “1.5+dfsg.1-3”.

* packaging: (30 commits)
  Finalise release “1.5+dfsg.1-3”.
  Document a published file that is not free software.
  Reformat the ‘README.source’ document.
  Ensure that a failure in any subprocess fails the pipeline.
  Clean up working root directory on any terminating signal.
  Update my email address for Debian work.
  Use correct override hooks for Debhelper 9.
  Simplify rules using Debhelper automatic targets.
  Update Debhelper compatibility to version 9.
  Add Lintian override for absence of UScan configuration file.
  Send HTTP traffic to the “discard” service during packaging actions.
  Make distinct rules for getting upstream source.
  Document recommendation for ‘get-orig-source’ target.
  Update copyright notice and descriptive comments.
  Declare “Standards-Version: 3.9.8”.
  Document “all rights granted” without assuming public domain.
  Distinguish license conditions from license grants.
  Update copyright notices.
  Add editor hints to ‘debian/copyright’.
  Remove superfluous override for Lintian.
  ...