Stringifies an entire row, filling in blanks with prior titles as they are found.

def _stringify_row(self, row_index):
        '''
        Stringifies an entire row, filling in blanks with prior titles as they are found.
        '''
        table_row = self.table[row_index]
        prior_cell = None
        for column_index in range(self.start[1], self.end[1]):
            cell, changed = self._check_interpret_cell(table_row[column_index], prior_cell, row_index, column_index)
            if changed:
                table_row[column_index] = cell
            prior_cell = cell