adaptiveMH or of pawl, and
component indices, and draws a 2D density plot with the first component on the x-axis and
the second on the y-axis.
PlotDensComp1vsComp2(results, comp1, comp2)"list": either the output of pawl or of adaptiveMH.
"numeric": specifies the index of the component to plot on the x-axis.
"numeric": specifies the index of the component to plot on the y-axis.
ggplot