Update EZID to demoinstrate testing with DataCite 4.0 XML documents.
This is mainly an update of testing and documentation, no feature changes. Now the tests demonstrate uploading both DataCite 3.1 and DataCite 4.0 metadata. Current DataCite 4.2 uploads are not working yet as they are not yet supported in EZID at CDL. No library changes here should be required for future DataCite metadata versions once the EZID service itself supports them.