Read and process CRF 2021 for v2.3

[JGuetschow]

Read and preprocess CRF 2021 data for v2.3

• [x] download initial version (May 2021)
• [x] check and adjust preprocessing if necessary
• [x] integrate into PRIMAP-hist
• [x] last update before cutoff for v2.3 (Aug. 1st 2021)
• [ ] check and publish on zenodo

[JGuetschow]

publication on zenodo will be skipped as there is no time for it.