code: def affiliation_history(self):
          
          affs = self._json.get('affiliation-history', {}).get('affiliation')
          try:
              return [d['@id'] for d in affs]
          except TypeError:  # No affiliation history
              return None
docs: Unordered list of IDs of all affiliations the author was
          affiliated with acccording to Scopus.