Merge pull request #283 from adafruit/scd30

adding the SCD30 eCO2 sensor

Author: ladyada

.gitmodules

@@ -757,3 +757,6 @@
 [submodule "libraries/helpers/portalbase"]
 	path = libraries/helpers/portalbase
 	url = https://github.com/adafruit/Adafruit_CircuitPython_PortalBase.git
+[submodule "libraries/drivers/scd30"]
+	path = libraries/drivers/scd30
+	url = https://github.com/adafruit/Adafruit_CircuitPython_SCD30.git

docs/drivers.rst

@@ -361,6 +361,7 @@ equivalent carbon dioxide (``eco2`` / ``eCO2``), and total volatile organic comp
     MS8607 Pressure, Temperature, Humidity <https://circuitpython.readthedocs.io/projects/ms8607/en/latest/>
     PCT2075 Temperature Sensor <https://circuitpython.readthedocs.io/projects/pct2075/en/latest/>
     PM25 Air Quality Sensor <https://circuitpython.readthedocs.io/projects/pm25/en/latest/>
+    SCD30 eCO2, Temperature, and Humidity Sensor <https://circuitpython.readthedocs.io/projects/scd30/en/latest/>
     SGP30 Air Quality <https://circuitpython.readthedocs.io/projects/sgp30/en/latest/>
     SHT31-D Temperature and Humidity <https://circuitpython.readthedocs.io/projects/sht31d/en/latest/>
     SHTC3 Temperature and Humidity <https://circuitpython.readthedocs.io/projects/shtc3/en/latest/>