Draw ridgeplot for each plotter.

        Parameters
        ----------
        mult : float
            How much to multiply height by. Set this to greater than 1 to have some overlap.
        linewidth : float
            Width of line on border of ridges
        alpha : float
            Transparency of ridges
        ax : Axes
            Axes to draw on

def ridgeplot(self, mult, linewidth, alpha, ax):
        """Draw ridgeplot for each plotter.

        Parameters
        ----------
        mult : float
            How much to multiply height by. Set this to greater than 1 to have some overlap.
        linewidth : float
            Width of line on border of ridges
        alpha : float
            Transparency of ridges
        ax : Axes
            Axes to draw on
        """
        if alpha is None:
            alpha = 1.0
        zorder = 0
        for plotter in self.plotters.values():
            for x, y_min, y_max, color in plotter.ridgeplot(mult):
                if alpha == 0:
                    border = color
                else:
                    border = "k"
                ax.plot(x, y_max, "-", linewidth=linewidth, color=border, zorder=zorder)
                ax.plot(x, y_min, "-", linewidth=linewidth, color=border, zorder=zorder)
                ax.fill_between(x, y_min, y_max, alpha=alpha, color=color, zorder=zorder)
                zorder -= 1
        return ax