Add support for printing on red/black tapes

My QL-800 refuses to print black only on a red/black tape.

I really don't like the added `rb` function parameter.
It would be best to be able to recognize such tapes, however
nothing of the sort is documented in official Brother documentation.

makeBitmapData{,RB} also look like they could be simplified further.

cmd/label-tool/main.go

@@ -211,7 +211,7 @@ func handle(w http.ResponseWriter, r *http.Request) {
 				font.Font, params.Text, mediaInfo.PrintAreaPins, params.Scale)
 		}
 		if r.FormValue("print") != "" {
-			if err := printer.Print(img); err != nil {
+			if err := printer.Print(img, false); err != nil {
 				log.Println("print error:", err)
 			}
 		}

cmd/ql-print/main.go

@@ -17,6 +17,7 @@ import (
 
 var scale = flag.Int("scale", 1, "integer upscaling")
 var rotate = flag.Bool("rotate", false, "print sideways")
+var redblack = flag.Bool("redblack", false, "red and black print")
 
 func main() {
 	flag.Usage = func() {
@@ -82,7 +83,7 @@ func main() {
 		log.Fatalln("the image is too high,", dy, ">", mi.PrintAreaLength, "pt")
 	}
 
-	if err := p.Print(img); err != nil {
+	if err := p.Print(img, *redblack); err != nil {
 		log.Fatalln(err)
 	}
 }

cmd/sklad/main.go

@@ -309,7 +309,7 @@ func printLabel(id string) error {
 	}
 
 	return printer.Print(&imgutil.LeftRotate{Image: label.GenLabelForHeight(
-		labelFont, id, mediaInfo.PrintAreaPins, db.BDFScale)})
+		labelFont, id, mediaInfo.PrintAreaPins, db.BDFScale)}, false)
 }
 
 func handleLabel(w http.ResponseWriter, r *http.Request) {