plot,plotter: introduce new NewLegend

legend.go

@@ -76,10 +76,9 @@ type Thumbnailer interface {
 	Thumbnail(c *draw.Canvas)
 }
 
-// NewLegend returns a legend with the default
-// parameter settings.
-func NewLegend() (Legend, error) {
-	return newLegend(DefaultTextHandler), nil
+// NewLegend returns a legend with the default parameter settings.
+func NewLegend() Legend {
+	return newLegend(DefaultTextHandler)
 }
 
 func newLegend(hdlr text.Handler) Legend {

legend_example_test.go

@@ -48,10 +48,7 @@ func ExampleLegend_standalone() {
 	green := exampleThumbnailer{Color: color.NRGBA{G: 255, A: 255}}
 	blue := exampleThumbnailer{Color: color.NRGBA{B: 255, A: 255}}
 
-	l, err := plot.NewLegend()
-	if err != nil {
-		panic(err)
-	}
+	l := plot.NewLegend()
 	l.Add("red", red)
 	l.Add("green", green)
 	l.Add("blue", blue)
@@ -90,6 +87,7 @@ func ExampleLegend_standalone() {
 		panic(err)
 	}
 	defer w.Close()
+
 	png := vgimg.PngCanvas{Canvas: c}
 	if _, err := png.WriteTo(w); err != nil {
 		panic(err)

plotter/heat_example_test.go

@@ -39,10 +39,7 @@ func ExampleHeatMap() {
 	p.Add(h)
 
 	// Create a legend.
-	l, err := plot.NewLegend()
-	if err != nil {
-		log.Panic(err)
-	}
+	l := plot.NewLegend()
 	thumbs := plotter.PaletteThumbnailers(pal)
 	for i := len(thumbs) - 1; i >= 0; i-- {
 		t := thumbs[i]