Added Add2D methods for PointF{,32}.

- Add2D adds x, y values instead of a point (Add).

pointf.go

@@ -22,6 +22,11 @@ func (p PointF) Add(q PointF) PointF {
 	return PointF{p.X + q.X, p.Y + q.Y}
 }
 
+// Add2D adds x and y to X and Y of point p and returns the sum.
+func (p PointF) Add2D(x, y float64) PointF {
+	return PtF(p.X+x, p.Y+y)
+}
+
 // AngleTo calculates the angle [0..2*Pi) from point p to point q.
 func (p PointF) AngleTo(q PointF) float64 {
 	a := math.Atan((p.Y - q.Y) / (p.X - q.X))

pointf32.go

@@ -22,6 +22,11 @@ func (p PointF32) Add(q PointF32) PointF32 {
 	return PointF32{p.X + q.X, p.Y + q.Y}
 }
 
+// Add2D adds x and y to X and Y of point p and returns the sum.
+func (p PointF32) Add2D(x, y float32) PointF32 {
+	return PtF32(p.X+x, p.Y+y)
+}
+
 // AngleTo calculates the angle [0..2*Pi) from point p to point q.
 func (p PointF32) AngleTo(q PointF32) float32 {
 	a := float32(math.Atan(float64((p.Y - q.Y) / (p.X - q.X))))