tone: add package for producing tones using the PWM interface

examples/tone/tone.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/tone"
+)
+
+var (
+	// Configuration for the Adafruit Circuit Playground Bluefruit.
+	pwm = machine.PWM0
+	pin = machine.D12
+)
+
+func main() {
+	speaker, err := tone.New(pwm, pin)
+	if err != nil {
+		println("failed to configure PWM")
+		return
+	}
+
+	// Two tone siren.
+	for {
+		println("nee")
+		speaker.SetNote(tone.B5)
+		time.Sleep(time.Second / 2)
+
+		println("naw")
+		speaker.SetNote(tone.A5)
+		time.Sleep(time.Second / 2)
+	}
+}