Merge all columns and place text string in widened cell.

def wr_row_mergeall(self, worksheet, txtstr, fmt, row_idx):
        """Merge all columns and place text string in widened cell."""
        hdridxval = len(self.hdrs) - 1
        worksheet.merge_range(row_idx, 0, row_idx, hdridxval, txtstr, fmt)
        return row_idx + 1