Mqtt-io

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- Add PCF8575 support. 121
- Add MCP3008 sensor support. 115
- Add AHT20 sensor support. 122
- Add BME280 sensor support. 132
- Install requirements using current Python executable. 134
- Add sensors to HASS discovery. 133
- Add option to publish output value on startup. 125

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- Update PyYAML to a version that doesn't suffer from CVE-2020-1747 vulnerability.
- Add 'stream' IO.

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- Pin safe version of PyYAML in requirements.

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- Merge PR from BenjiU which implements a new sensor interface. 52

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- Add cleanup function to modules which are called before program exit. 16

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- Decode received MQTT message payload as utf8 before trying to match with on/off payload values. 14