Remove microbit matrix (#319)

* Remove matrix code from bbc:microbit, and move it to a driver

src/examples/microbit-blink/microbit-blink.go

@@ -1,4 +1,4 @@
-// blink program for the BBC micro:bit that uses the entire LED matrix
+// blink program for the BBC micro:bit
 package main
 
 import (
@@ -6,14 +6,19 @@ import (
 	"time"
 )
 
+// The LED matrix in the micro:bit is a multiplexed display: https://en.wikipedia.org/wiki/Multiplexed_display
+// Driver for easier control: https://github.com/tinygo-org/drivers/tree/master/microbitmatrix
 func main() {
-	machine.InitLEDMatrix()
-
+	ledrow := machine.GPIO{machine.LED_ROW_1}
+	ledrow.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
+	ledcol := machine.GPIO{machine.LED_COL_1}
+	ledcol.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
+	ledcol.Low()
 	for {
-		machine.ClearLEDMatrix()
+		ledrow.Low()
 		time.Sleep(time.Millisecond * 500)
 
-		machine.SetEntireLEDMatrixOn()
+		ledrow.High()
 		time.Sleep(time.Millisecond * 500)
 	}
 }