Select and Download Climate Data from 'DWD' (German Weather Service)

Handle climate data from the 'DWD' ('Deutscher Wetterdienst', see < https://www.dwd.de/EN/climate_environment/cdc/cdc.html> for more information). Choose files with 'selectDWD()', download and process data sets with 'dataDWD()' and 'readDWD()'.