Added a SHT31 humidity/temp sensor, and tweaked some more. CO2 experiments soon...

[S1] CO2: 414ppm, TVOC: 2ppb, baseLine: 0xADC1 (0xA8C0), lErr: 0b0
[S2] Pressure: 100629.10Pa, Temp: 32.71C
[S3] External temp: 31.69C
[S4] Humidity: 55.96%, Temp: 32.76C
Uptime: 1966s