Fence plots combine several 2D plots by aligning their Y coordinates and
separating them from each other by a displacement along X. Filling the area
between a base value and each plot's series of Z values enhances the visual
impact of the alignment on Y and comparison on Z. There are several ways
such plots can be created in gnuplot. The simplest is to use the 5 column
variant of the zerrorfill style. Suppose there are separate curves z = Fi(y)
indexed by i. A fence plot is generated by splot with zerrorfill using
input columns
i y z_base z_base Fi(y)
