examples: clean up examples and add blinky1 for Arduino

Arduino has trouble supporting anything that's not extremely simple, so
add a simple blinky example for it. Also, it may be useful anyway.

src/examples/blinky1/blinky1.go

@@ -0,0 +1,20 @@
+package main
+
+// This is the most minimal blinky example and should run almost everywhere.
+
+import (
+	"machine"
+	"runtime"
+)
+
+func main() {
+	led := machine.GPIO{machine.LED}
+	led.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
+	for {
+		led.Low()
+		runtime.Sleep(runtime.Millisecond * 500)
+
+		led.High()
+		runtime.Sleep(runtime.Millisecond * 500)
+	}
+}