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/blinky2/blinky2.go

@@ -0,0 +1,44 @@
+package main
+
+// This blinky is a bit more advanced than blink1, with two goroutines running
+// at the same time and blinking a different LED. The delay of led2 is slightly
+// less than half of led1, which would be hard to do without some sort of
+// concurrency.
+
+import (
+	"machine"
+	"runtime"
+)
+
+func main() {
+	go led1()
+	led2()
+}
+
+func led1() {
+	led := machine.GPIO{machine.LED}
+	led.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
+	for {
+		println("+")
+		led.Low()
+		runtime.Sleep(runtime.Millisecond * 1000)
+
+		println("-")
+		led.High()
+		runtime.Sleep(runtime.Millisecond * 1000)
+	}
+}
+
+func led2() {
+	led := machine.GPIO{machine.LED2}
+	led.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
+	for {
+		println("  +")
+		led.Low()
+		runtime.Sleep(runtime.Millisecond * 420)
+
+		println("  -")
+		led.High()
+		runtime.Sleep(runtime.Millisecond * 420)
+	}
+}