Moves the turtle along an arc (part of a circle).
The arc sweeps an amount given by the
The size (curvature) of the arc is based on the
angle is positive, then the turtle moves forward in a clockwise direction.
angle is negative, then the turtle moves backward in a counter-clockwise direction.
; a 2D example ARC2 360 100 ARC2 90 50
; a 3D example PERSPECTIVE REPEAT 36 [RIGHTROLL 10 ARC2 180 100 ARC2 -180 100]