Nested get

It would be good to be able to use more advnced notions for getting nested items.

For nested JSON:
```
    {
        "A" : 5,
        "B" : {
                    "B1" : 7
                 }
    }
```

Given "B.B1" we should get "7".

Since the get is a Map method we can provide a "fetch" method.

