Document how to use the FirebaseObject's operator[] methods.

[ed7coyne]

Document how to use these, both in the code and in an example. It it not entirely intuitive what they are doing. I assume you can do something like FirebaseObject["some_key"] = some_value but why are there three of them and what are the subtle differences with their return types?

[ed7coyne]

We are dropping these so this issue is no longer applicable.