Basic marker drawing primitive.
POLYMARK is obsolete, but provided for upward compatibility from
POLYMARK(X,Y) draws polymarkers at the X- and Y-coordinates
in vectors X and Y.
POLYMARK(X,Y,'type') uses the marker style and color
indicated by the text string. See PLOT for a list of
style and color attributes.
POLYMARK(X,Y,'sc') interprets X and Y in screen-coordinates
where (0.0,0.0) is the lower-left corner of the screen and
(1.0,1.0) is the upper-right corner. Otherwise, data-
coordinates are used.