Adds a series to the chart.
        
        :param values: A :py:class:`xltable.Expression` object that evaluates to the data series.
        :param categories: A :py:class:`xltable.Expression` object that evaluates to the data series.
        :param name: Name to show in the legend for the series
        :param line: Line style, eg {'color': 'blue', 'width': 3.25} or {'none': True}
        :param marker: dict specifying how the markers should look, eg {type: square}.
        :param trendline: dict specifying how the trendline should be drawn, eg {type: linear}.

def add_series(self, values, **kwargs):
        """
        Adds a series to the chart.
        
        :param values: A :py:class:`xltable.Expression` object that evaluates to the data series.
        :param categories: A :py:class:`xltable.Expression` object that evaluates to the data series.
        :param name: Name to show in the legend for the series
        :param line: Line style, eg {'color': 'blue', 'width': 3.25} or {'none': True}
        :param marker: dict specifying how the markers should look, eg {type: square}.
        :param trendline: dict specifying how the trendline should be drawn, eg {type: linear}.
        """
        series = {"values": values}
        series.update(kwargs)
        self.__series.append(series)