docs: def history(self, dates=None, linreg_since=None, lin_reg_days=20):
          '''
          Works only on a Result that has _start and _end columns.
  
          :param dates: list of dates to query
          :param linreg_since: estimate future values using linear regression.
          :param lin_reg_days: number of past days to use as prediction basis
          '''
          dates = dates or self.get_dates_range()
          vals = [self.on_date(dt, only_count=True) for dt in dates]
          ret = Series(vals, index=dates)
          if linreg_since is not None:
              ret = self._linreg_future(ret, linreg_since, lin_reg_days)
          return ret.sort_index()