It would be too easy if we could just call sorted(). Thanks to zone
grammar the most important key "type" gets sorted near end, so we pull
it up to the top using a hack.
It turns out the tree of dictionaries is not the best structure to
represent our grammar, unfortunatelly. The problem is that "zone" has
several context-dependent variants which change meaning of "zone" based
on inner field "type".
Redesigning the whole structure does not seem to be worth, so I settled
on this terrible hack.
The utility detects statements which use the same name (e.g.
max-zone-ttl) but use different grammar in different contexts. These
typically need special case in docs.
