clinicaltrials_gov_dates
                        Download a table 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
extract_publications    Takes a data frame of the type provided by
                        'clinicaltrials_gov_download()' and returns a
                        new data frame containing one row per
                        publication of the publication type specified
                        indexed on ClinicalTrials.gov for every version
                        of the clinical trial record provided.
overall_status_lengths
                        Interpret downloaded version histories to
                        determine how long in days a trial had any
                        given overall status
