Adds a chart to the worksheet at (row, col).

        :param xltable.Chart Chart: chart to add to the workbook.
        :param int row: Row to add the chart at.

def add_chart(self, chart, row, col):
        """
        Adds a chart to the worksheet at (row, col).

        :param xltable.Chart Chart: chart to add to the workbook.
        :param int row: Row to add the chart at.
        """
        self.__charts.append((chart, (row, col)))