add tests for onoff

onoff/onoff-tests.ts

@@ -0,0 +1,16 @@
+import * as onoff from 'onoff';
+
+var led:onoff.Gpio = new onoff.Gpio(17, 'out');
+
+var toggleLed = function():void {
+    var lastState:number = led.readSync();
+    led.writeSync(lastState ^ 1);
+};
+
+var intervalId:number = setInterval(toggleLed, 100);
+
+setTimeout(function() {
+    clearInterval(intervalId);
+    led.writeSync(0);
+    led.unexport();
+}, 2000);