Simple line follower to get people started

Just thinking this through:

```javascript
var calibrating = true;
var running = false;

stdin.on("keypress", function() {
  calibrating = false;
  running = !running;

  if(!running) wheels.stop();
});

eyes.on("line", function(err, line) {
  if(!running) return;

  // handle line data
});
```