Modifying a flexbuffers Map after loading from JSON

[nathanmartz]

I would like to create a flexbuffers Map from a JSON string and then modify some of the elements of that map, including Maps contained within that Map. From what I can tell, the only way to do this is to use a builder to create a new Map that contains both the original Map data and the values I want to add/modify. I've written the code to do this, but my currently implementation is a bit more complicated than I would like, so I wanted to see if there was a simpler way to simply modify a Map.