Borgmatic

* 437: Fix error when configuration file contains "umask" option.
* Remove test dependency on vim and /dev/urandom.

* 379: Suppress console output in sample crontab and systemd service files.
* 407: Fix syslog logging on FreeBSD.
* 430: Fix hang when restoring a PostgreSQL "tar" format database dump.
* Better error messages! Switch the library used for validating configuration files (from pykwalify
to jsonschema).
* Link borgmatic Ansible role from installation documentation:
https://torsion.org/borgmatic/docs/how-to/set-up-backups/#other-ways-to-install

* 419: Document use case of running backups conditionally based on laptop power level:
https://torsion.org/borgmatic/docs/how-to/backup-to-a-removable-drive-or-an-intermittent-server/
* 425: Run arbitrary Borg commands with new "borgmatic borg" action. See the documentation for
more information: https://torsion.org/borgmatic/docs/how-to/run-arbitrary-borg-commands/

* 390: Add link to Hetzner storage offering from the documentation.
* 398: Clarify canonical home of borgmatic in documentation.
* 406: Clarify that spaces in path names should not be backslashed in path names.
* 423: Fix error handling to error loudly when Borg gets killed due to running out of memory!
* Fix build so as not to attempt to build and push documentation for a non-main branch.
* "Fix" build failure with Alpine Edge by switching from Edge to Alpine 3.13.
* Move borgmatic IRC channel from Freenode to Libera Chat due to Freenode takeover drama.
IRC connection info: https://torsion.org/borgmatic/#issues

* 373: Document that passphrase is used for Borg keyfile encryption, not just repokey encryption.
* 404: Add support for ruamel.yaml 0.17.x YAML parsing library.
* Update systemd service example to return a permission error when a system call isn't permitted
(instead of terminating borgmatic outright).
* Drop support for Python 3.5, which has been end-of-lifed.
* Add support for Python 3.9.
* Update versions of test dependencies (test_requirements.txt and test containers).
* Only support black code formatter on Python 3.8+. New black dependencies make installation
difficult on older versions of Python.
* Replace "improve this documentation" form with link to support and ticket tracker.

* Fix for previous release with incorrect version suffix in setup.py. No other changes.