clinicaltrials_gov_dates
                        Download a vector of dates on which a
                        ClinicalTrials.gov registry entry was updated
clinicaltrials_gov_download
                        Mass-download registry entry historical
                        versions from ClinicalTrials.gov
clinicaltrials_gov_version
                        Download a registry entry version from
                        ClinicalTrials.gov
drks_de_dates           Download a vector of dates on which a drks.de
                        registry entry was updated
drks_de_download        Mass-download registry entry historical
                        versions from DRKS.de
drks_de_version         Download a registry entry version from DRKS.de
