    g.Curve(p1 [, p2, p3, p4])

Return a new curve object with start at point `p1`, control points at `p2` and `p3`, and end at `p4`. All points are passed through the `Point` constructor so they can also be passed in string form. Examples:

    var c = new g.Curve(new g.Point(10, 10), new g.Point(10, 40), new g.Point(50, 40), new g.Point(50, 10));
    var c = new g.Curve('10 10', '10 40', '50 40', '50 10');
    var c = new g.Curve('10@10', '10@40', '50@40', '50@10');

The constructor also accepts a single Curve object as an argument; it creates a new curve with points cloned from the provided curve.