angle

fun angle(ax: Double, ay: Double, bx: Double, by: Double, up: Vector2D = UP): Angle
fun angle(x1: Double, y1: Double, x2: Double, y2: Double, x3: Double, y3: Double, up: Vector2D = UP): Angle
fun angle(a: Vector2D, b: Vector2D, up: Vector2D = UP): Angle
fun angle(p1: Vector2D, p2: Vector2D, p3: Vector2D, up: Vector2D = UP): Angle