FunTuple - add a handy function to dump structure of branches and variables?

For debugging purposes it would be great if one would be able to get a dict (or alike) specifying the full structure of branches (fields) and variables defined when instantiating FunTuple. Seems like an extremely useful thing to have (also for unit tests and alike, BTW!). That should contain the user-defined variables and those refering to "ALL".

At this point I don't know how easy that is. To be discussed. Just a thought.