Yacron

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* Build a standalone Linux binary, using PyOxidizer
* Switch from raven to sentry-sdk

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* Added an option to just check if the yaml file is valid without running the scheduler.
* Fix missing `body` in the schema for sentry config

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* Fix a bug handling ``reboot`` in schedule (22)

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* Sentry: add new ``extra`` and ``level`` options.

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* Added the ``utc`` option and document that times are utc by default (17);
* If an email body is empty, skip sending it;
* Added docker and k8s example.

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* Add custom Sentry fingerprint support
* Ability to send job metrics to statsd (thanks bofm)
* ``always`` flag to consider any cron job that exits to be failed
(thanks evanjardineskinner)
* `maximumRetries` can now be ``-1`` to never stop retrying (evanjardineskinner)
* ``schedule`` can be the string ``reboot`` to always run that cron job on startup
(evanjardineskinner)
* ``saveLimit`` can be set to zero (evanjardineskinner)