- Better handling of server errors
+ Instead of using hard coded exception messages for assumed server errors, a single server error exception now includes the server's error message, if available.
- It is now possible to use the `shallow` parameter when performing a GET request. See [the Firebase Docs on Query Parameters](https://www.firebase.com/docs/rest/api/#section-query-parameters) for a detailed description.
- `Firebase::push()` now returns the generated key as a string (not as an array `['name' => '...']`) anymore