* Add concurrent downloads to downloader.
* Moved to Go 1.20
* close files channel on producer side.
* Improve error handling
* New flag to ignore signature check results. Improve docs. Do not use number of CPUs to determine number of download workers.
* Set number of default workers in downloader to two.
* make it more clear that a domain can also be interpreted as a direct URL.
resolve #316
---------
Co-authored-by: JanHoefelmeyer <hoefelmeyer.jan@gmail.com>
Co-authored-by: Sascha L. Teichmann <sascha.teichmann@intevation.de>
Co-authored-by: Bernhard Reiter <bernhard@intevation.de>