Skip printing of non-presence containers and list entries

[jktjkt]

The default printer produces a lot of data:

• non-presence containers are printed
• in case of lists, the "mostly useless" items are:
  • the list entry itself
  • explicit entries about list keys (but be careful when removing them in case of lists that only has keys, for example)

In short, the shorter the output the better, IMHO.