
fltk.fl_curve(x1,y1,x2,y2,x3,y3,x4,y4)
x1,y1 and x4,y4 specify the start and end of the curve.

This demostration uses 2 curves. The end point of the first
curve shares the same coordinates as the start point of the
second curve so it appears as though the curves are joined.

I don't know if there is a simpler way to clear drawings.
I thought simply redrawing the display area would work,
but that seems to prevent anything from displaying over it.
