Emit an event when a view is created

I'm not sure if this is the correct way to do it but I didn't found another solution. This basically allows manipulating the view object when a new Ripple instance is created:

```js
Ripple.on('construct', function (View) {
})
```

Maybe `construct` is not the best name and I should have called it `instance` or something. This would also allow [ripple-router#34](https://github.com/queckezz/ripple-router/blob/master/index.js#L34) to work.

What do you think?