* Added the ability to Weather Underground to track severe weather alerts
* * Added message on the advisory attr
* Updated tests
* * Making use of guard clause
* Checking multiple_alerts prior loop
* Using a better way to create dict
* Fixed issue to set to None only the object that failed
* Added unittest
* Split update() method to different calls with their one throttle control to minimize API calls
* Updated unittest and make sure the alert sensor will not return 'unknown' status'
* Removed update() method from state property
* Branch rebased and include Weather Underground attribution
* Update wunderground.py
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