Python library to retrieve climate statistics from DWD CDC.

Date provided by Climate Data Center (CDC) of Deutscher WetterDienst (DWD)
are retrieved from opendata.dwd.de and simple statistics on
hourly, daily and monthly basis are calulated.

Statistics are returned matching a provided list of dates.

The statistics are cached in the user home directory for subsequent calls.
The DWD server is regularly checked for updates and statistics are updated,
if necessary. Updates can be triggerd manually, too.
