code: public TreeMap<Integer, T_PreKey> generateOmemoPreKeys(int startId, int count) {
          return keyUtil().generateOmemoPreKeys(startId, count);
      }
docs: Generate 'count' new PreKeys beginning with id 'startId'.
  These preKeys are published and can be used by contacts to establish sessions with us.
  
  @param startId start id
  @param count   how many keys do we want to generate
  @return Map of new preKeys