Return |_Cell| instance correponding to table cell at *row_idx*,
        *col_idx* intersection, where (0, 0) is the top, left-most cell.

def cell(self, row_idx, col_idx):
        """
        Return |_Cell| instance correponding to table cell at *row_idx*,
        *col_idx* intersection, where (0, 0) is the top, left-most cell.
        """
        cell_idx = col_idx + (row_idx * self._column_count)
        return self._cells[cell_idx]