plstripa: Add a point to a stripchart 

DESCRIPTION:

    Add a point to a given pen of a given stripchart. There is no need for
    all pens to have the same number of points or to be equally sampled in
    the x coordinate. Allocates memory and rescales as necessary. 

SYNOPSIS:

plstripa(id, p, x, y)

ARGUMENTS:

    id (PLINT, input) :    Identification number (set up in plstripc) of
    the stripchart. 

    p (PLINT, input) :      Pen number (ranges from 0 to 3). 

    x (PLFLT, input) :      X coordinate of point to plot. 

    y (PLFLT, input) :      Y coordinate of point to plot.