pljoin: Draw a line between two points 

DESCRIPTION:

    Joins the point (
    x1, 
    y1) to (
    x2, 
    y2). 

SYNOPSIS:

pljoin(x1, y1, x2, y2)

ARGUMENTS:

    x1 (PLFLT, input) :    x coordinate of first point. 

    y1 (PLFLT, input) :    y coordinate of first point. 

    x2 (PLFLT, input) :    x coordinate of second point. 

    y2 (PLFLT, input) :    y coordinate of second point.