Calypso-anemometer

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- Rename ``reading.compass`` to ``reading.heading`` for better "naming things"
- SignalK telemetry: Use Radian (rad) unit for angle values
- SignalK telemetry: Use Kelvin unit for temperature
- SignalK telemetry: Use ratio (percentage) for battery level
- Compass: Add ``--compass=on`` option to enable compass
- NMEA0183 telemetry: Use ``$MLVWR`` sentence prefix for wind data
- NMEA0183 telemetry: Emit compass/heading data using ``$MLHDT`` sentence
- NMEA0183 telemetry: Emit compass/pitch+roll data using ``$MLXDR`` sentence
- NMEA0183 telemetry: Emit air temperature and battery level data using ``$MLXDR`` sentences
- Project metadata: Migrate from ``setup.py`` to ``pyproject.toml``

Thanks to UserMacUseface and honigwald for providing excellent domain
knowledge and bug reports.

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- Fix import error ``ModuleNotFoundError: No module named 'aiorate'``
- Configure minimum log level to ``WARNING`` when using the ``--quiet`` option

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Changes
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- Fix import error on Python 3.7
``AttributeError: module 'asyncio' has no attribute 'exceptions'``
- Add a few more software tests
- Add a few example programs
- Drop support for Python 3.6
- Add ``make lint`` sandbox utility task
- Emit ``CalypsoDecodingError`` exceptions when decoding wire data fails
- Refactor workhorse functions from ``cli.py`` to ``engine.py``
- Significantly improve test coverage
- Introduce ``Settings``, to bundle configuration settings
through command line options or environment variables.

- ``--ble-adapter`` / ``CALYPSO_BLE_ADAPTER``
- ``--ble-address`` / ``CALYPSO_BLE_ADDRESS``
- ``--ble-discovery-timeout`` / ``CALYPSO_BLE_DISCOVERY_TIMEOUT``
- ``--ble-connect-timeout`` / ``CALYPSO_BLE_CONNECT_TIMEOUT``
- Add ``--quiet`` option / ``CALYPSO_QUIET`` environment variable for
silencing output to STDOUT
- Explicitly use little-endian byte order for decoding binary data

Breaking changes
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- The ``CALYPSO_ADDRESS`` environment variable has been renamed to
``CALYPSO_BLE_ADDRESS``.

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- Telemetry: Generate fake device readings, for supplying synthetic data

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- CI: Run software tests on GHA
- Fix installation on Python 3.6
- NMEA-0183: Fix computing ``LR`` direction indicator
- NMEA-0183: Compute missing ``speed_`` from other ``speed_`` values
- NMEA-0183: Implement checksum
- Telemetry: Synthesize zeroing of wind direction, when wind speed goes zero

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- Add software tests for telemetry subsystem
- NMEA-0183: Fix message structure
- NMEA-0183: Fix wind direction and add "left/right of bow" indicator
- Fix reading/decoding data rate
- Optimize discovery: Stop scanning when device was found