Allow for a partial parse

[eike]

It would be great if there were a way to partially parse a JSON. For example, I imagine a call like

dict = JSON3.read("""
{
  "a": { "foo": 1 },
  "b": { "bar": 2 },
}""", Dict{String, JSON3.Partial})

where the result would be a Dict with the two keys "a" and "b" and values representing the two inner dictionaries. Then, you could later call JSON3.read(dict["a"], some_type) to further parse the sub-results.

The point is to postpone the decision on how to parse the inner dictionaries; for example, their target types could depend on the keys (or each other) in complex ways.

I have the impression that this is almost possible with RawType and RawValue, but if it is, I can’t figure out how.