rugs.gle
Subroutines to draw x- and y-axis rugs.
Author: Francois Tonneau
List of subroutines:
xrug: draw rugs along the x axes.
yrug: draw rugs along the y axes.
Warning: Do not use xrug or yrug on datasets with missing values. Because
GLE's dataxvalue() and datayvalue() interpret absent numbers as 0, xrug and
yrug will draw a 0-based tick for each nonexistent x or y.
It is best to call xrug or yrug after the corresponding graph block is over.
Calling xrug or yrug from a graph block with 'draw' would probably clip the
rugs, which is not what you want.