Allow to add a JSON by reference, not only FileURL

Hey, I have added a new option for init abjson:

```javascript
var json = {
   "hello": "world"
};

abjson.init({
    source : json,
  }, function(err){
    $(body).abjson();
});
```

So, if I already have my config JSON file on client-side, I can still use some Vodka ;)