Mqttwarn

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- srv.mqttc is None when calling into a custom function. Thanks, Ben.
- sundry changes for FreeBSD package. Thanks, Dan.
- Fix ``ZabbixSender.py``. Thanks, Ben!
- service tweaks: nsca, zabbix

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- Optionally choose scheme for connection to InfluxDB. Thanks, Dennis!

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- Fix charset encoding within pipe module. Thanks, Morten!
- Fix removal of "as_user" option within Slack plugin. Thanks, Morten!

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- Fix for the mqttwarn.service service unit. Thanks, Fulvio!
- Fix encoding of data for Python3 within Pushsafer plugin. Thanks, Thomas!
- Non-JSON payload should not generate warning. Thanks, Morten!
- Fix missing namespace within Serial plugin. Thanks, Morten!
- Fix Dockerfile to use mqttwarn pip module. Thanks, Koen!
- Add Docker Compose file and update Dockerfile to use /etc/mqttwarn. Thanks, Koen!
- Change Dockerfile base image to python:3.8.2-slim-buster. Thanks, Koen!
- Improve code formatting within custom functions of "warntoggle" example. Thanks, Dan!
- Fix charset encoding within Serial plugin. Thanks, Morten!

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- Document ``tls=True`` setting. Thanks, jpmens!
- Add ``warntoggle`` example (408). Thanks, robdejonge!
- Load functions file at configuration load (410). Thanks, fhriley!
- Try to make "zabbix" service work again

=================
- Upgrade to apprise 0.8.5