Test whether a point is to the left or the right of a curve.

Input parameters:

1. Pt → Point for curve side test.
2. Cr → Guide curve.
3. Pl → Optional override for testing plane. If omitted, the curve plane is used.

Output parameters:

1. Le → True if the shape is to the left of the curve.
2. Ri → True if the shape is to the right of the curve.