Deserialization: Option to have object libs stay where they are

[madig]

In iondrive, I have to reverse norad's automatic extraction of object libs into .lib fields. It would be easier if I could just pass the data through unchanged.

[madig]

Maybe this can be a DataRequest field.

[cmyr]

If it makes more sense to leave these libs in place, then we should do that, but I'm not in favour of making it an option unless there's a really compelling rationale. In my experience this sort of thing just makes the code more complicated and makes using the crate more error prone.