/* Add an arc of a circle to the context's path, possibly preceded by a
straight line segment. `(x, y)' is the center of the arc; `radius' is its
radius; `startAngle' is the angle to the first endpoint of the arc;
`endAngle' is the angle to the second endpoint of the arc; and
`clockwise' is 1 if the arc is to be drawn clockwise, 0 otherwise.
`startAngle' and `endAngle' are measured in radians. */
@available(iOS 2.0, *)
public func CGContextAddArc(c: CGContext?, _ x: CGFloat, _ y: CGFloat, _ radius: CGFloat, _ startAngle: CGFloat, _ endAngle: CGFloat, _ clockwise: Int32)