The impulses style displays a vertical line from y=0 to the y value of each
point (2D) or from z=0 to the z value of each point (3D). Note that the y or z
values may be negative. Data from additional columns can be used to control
the color of each impulse. To use this style effectively in 3D plots, it is
useful to choose thick lines (linewidth 5#5 1). This approximates a 3D bar chart.
1 column: y
2 columns: x y # line from [x,0] to [x,y] (2D)
3 columns: x y z # line from [x,y,0] to [x,y,z] (3D)
