f32: implement fmt.Stringer to Point and Rectangle

Signed-off-by: Wagner Riffel <wgrriffel@gmail.com>

f32/f32.go

@@ -9,17 +9,30 @@ corner with the axes extending right and down.
 */
 package f32
 
+import "strconv"
+
 // A Point is a two dimensional point.
 type Point struct {
 	X, Y float32
 }
 
+// String return a string representation of p.
+func (p Point) String() string {
+	return "(" + strconv.FormatFloat(float64(p.X), 'f', -1, 32) +
+		"," + strconv.FormatFloat(float64(p.Y), 'f', -1, 32) + ")"
+}
+
 // A Rectangle contains the points (X, Y) where Min.X <= X < Max.X,
 // Min.Y <= Y < Max.Y.
 type Rectangle struct {
 	Min, Max Point
 }
 
+// String return a string representation of r.
+func (r Rectangle) String() string {
+	return r.Min.String() + "-" + r.Max.String()
+}
+
 // Add return the point p+p2.
 func (p Point) Add(p2 Point) Point {
 	return Point{X: p.X + p2.X, Y: p.Y + p2.Y}