Borgmatic

* 73: Enable consistency checks for only certain repositories via "check_repositories" option in
borgmatic's consistency configuration. Handy for large repositories that take forever to check.
* Include link to issue tracker within various command output.
* Run continuous integration tests on a matrix of Python and Borg versions.

* 98: Support for Borg --keep-secondly prune option.
* Use Black code formatter and Flake8 code checker as part of running automated tests.
* Add an end-to-end automated test that actually integrates with Borg.
* Set up continuous integration for borgmatic automated tests on projects.evoworx.org.

* Fix generated configuration to also include a "keep_daily" value so pruning works out of the
box.

* 57: When generating sample configuration with generate-borgmatic-config, comment out all
optional configuration so as to streamline the initial configuration process.

* Fix for archive checking traceback due to parameter mismatch.

* 64, 90, 92: Rewrite of logging system. Now verbosity flags passed to Borg are derived from
borgmatic's log level. Note that the output of borgmatic might slightly change.
* Part of 80: Support for Borg create --read-special via "read_special" option in borgmatic's
location configuration.
* 87: Support for Borg create --checkpoint-interval via "checkpoint_interval" option in
borgmatic's storage configuration.
* 88: Fix declared pykwalify compatibility version range in setup.py to prevent use of ancient
versions of pykwalify with large version numbers.
* 89: Pass --show-rc option to Borg when at highest verbosity level.
* 94: Support for Borg --json option via borgmatic command-line to --create archives.