返回历史成交

        Arguments:
            start {str} -- [description]
            end {str]} -- [description]

def get_history(self, start, end):
        """返回历史成交

        Arguments:
            start {str} -- [description]
            end {str]} -- [description]
        """
        return self.history_table.set_index(
            'datetime',
            drop=False
        ).loc[slice(pd.Timestamp(start),
                    pd.Timestamp(end))]