V0.4 peanuts store update or add

resolves #134

if object `doc/123` does not exist, this will now fail with a `not found` error:

```js
hoodie.store.update('doc', '123', {title: 'funky!'});
```

To get the old behavior, use

```js
hoodie.store.updateOrAdd('doc', '123', {title: 'funky!'});
```