Two new example programs to plot CO2 data from Sensirion SCD-30 using Adafruit libraries

[kevinjwalters]

Two new programs for #25 to plot CO2 from (Adafruit) Sensirion SCD-30 using https://github.com/adafruit/Adafruit_CircuitPython_SCD30 library.

• examples/plotter_scd30.py - plot up to 3000ppm. 1b95f08f60282727a4482948d7bbb395cbe6ada2 064cb2564ef402e1ec738afb02020a33725feba3
• examples/plotters_combined_with_scd30.py - fourth optional plot page based on the adafruit_scd30 library being present and the SCD30 object initialises ok, i.e. device is plugged in and responding over i2c. This version also passes the pressure to the SCD-30. 5af87611c242bd68ea7396c502ff84257e08e719 8e5377a40c825a8359e67b8765b55605f53d455b

The combined one is a new file rather put all the functionality into plotters_combined.py as that's getting a little large in memory usage terms and SCD-30 users are probably in the minority.

Tested on a Feather nRF52840 Express running 6.2.0 and brand new Enviro+ FeatherWing: Plotting Carbon Dioxide concentration with Enviro+ FeatherWing and Sensirion SCD-30 NDIR Sensor (YouTube).

https://github.com/pimoroni/EnviroPlus-FeatherWing/pull/26/commits/288953d6001538370d0e829b3f4828a81c74e31c is same type of bugfix as https://github.com/pimoroni/EnviroPlus-FeatherWing/pull/24/commits/0c2cf96455fc9a396bd7e444d476503bfd2230c6

[kevinjwalters]

I'll update the REFERENCE.md file when #20 is approved and applied.

[kevinjwalters]

The SCD-30 library supports passing the pressure and since this is available from the BME280 I added that to plotters_combined_with_scd30.py.

[kevinjwalters]

Can be seen in action on Instructables: Plotting Carbon Dioxide Levels With the Pimoroni Enviro+ FeatherWing and Adafruit SCD-30.

[Gadgetoid]

Again, sorry for the radio silence here. This effort is very, very much appreciated.