Pro Custodibus Agent 1.6.0

Added
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* New extra helper scripts for WireGuard Pre/Post/Up/Down fields
  (located in `scripts` directory).
* New `OneLineFields = true` agent configuration setting to force
  WireGuard configuration fields that may use multiple lines
  (like `Address`, `AllowedIPs`, etc) to instead be written on
  one single line. Defaults to `false`.
* Allow WireSock to be used in place of WireGuard.

Changed
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* Allow `PROCUSTODIBUS_LOGGING_LEVEL` environment variable to override
  command line `--verbosity` (or `-v` or `-vv`) flags.
* Log new WireGuard config at debug level when updating it.
* Omit logging WireGuard service status on Windows when OK.

Fixed
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* Fix updates to WireGuard DNS setting when search path not specified.
* Fix configuration reloading on Windows.
* Resume regular ping loop faster after connectivity interruptions.
* Gracefully handle errors from missing agent credentials file.

Removed
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* Removed Python 3.7 as a supported version.