machine/usb: rename 'New()' to 'Port()' to have the API better match the singleton that is actually being returned

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/examples/usb-midi/main.go

@@ -17,7 +17,7 @@ func main() {
 	button := machine.BUTTON
 	button.Configure(machine.PinConfig{Mode: machine.PinInputPullup})
 
-	m := midi.New()
+	m := midi.Port()
 	m.SetHandler(func(b []byte) {
 		led.Set(!led.Get())
 		fmt.Printf("% X\r\n", b)