Add autoclosing feature for browser tabs


![pr](https://cloud.githubusercontent.com/assets/2142829/5423690/9698497c-82ca-11e4-9b1a-39a24285c099.gif)
Close the tab on `kill`.
`kill` is triggered when the livedown server shuts down.
can you change this to 

```js
 window.open('', '_self', '');
 window.close();
```

to workaround security issues for Chrome, since `window.close()` displays this message
> Scripts may close only the windows that were opened by it.