Simple (US) EPA AQI lookup

Simple check/lookup tool for US EPA PM 2.5 AQI (rather than raw PM2.5 in ug/m3). See "Air Quality Communication Workshop - San Salvador, El Salvador, April 16-17, 2012" https://www.epa.gov/sites/production/files/2014-05/documents/zell-aqi.pdf for details.

Initial support for:

• IQair / AirNow
  • https://www.airnow.gov/ https://docs.airnowapi.org/
• https://aqicn.org
• PurpleAir
  • https://www2.purpleair.com/community/faq#!hc-access-the-json
  • https://www.purpleair.com/sensorlist
  • https://docs.google.com/document/d/15ijz94dXJ-YAZLi9iZ_RaBwrZ4KtYeCy08goGBwnbCU/edit?usp=sharing
• Alert/notification support - via mqtt