New features

380 Implemented National Weather Alerts support
376 Now PyOWM uses SQLite instead of files to internally store city data. CityIDRegistry interface has changed but in a retrocompatible way

Enhancements

381 Now it is possible to specify how many times to retry an API call

Bugfixes

379 Experimental fix for 404 errors on Agromonitor API satellite image search
387 Fixed lat/lon swap bug on Airpollution API
389 Fixed wrong city name in City ID database