Cedar-backup3

* Improve logged output for failed pre/post action hooks.

* Standardize format of GPL license statement in CREDITS.

* Make minor structural improvements to the build process.
* Publish coverage data to coveralls.io in GitHub workflow.

* Always use '/' internally for paths, even on the Windows platform.
* Change the way archive filenames are generated to eliminate leading '-' characters.
* Use UTF-8 encoding for log files on disk to avoid problems with unusual filenames.
* Update build process to include security scans using Safety.

* Fix a couple of links in docs/index.rst (cut-and-paste error).

* Move to newer build dependencies (Black, isort, etc.).
* Make adjustments to code formatting to match new Black version.
* Force docs/requirements.txt to have UNIX line endings
* Convert to PEP 440 convention for Git tags (i.e. "v3.5.3").
* Standardize and improve badges in markdown, so they are all links.
* Simplify pylint configuration and use "-j 0" to speed it up.