TODO: more pprint imporvements

TODO

• dicts with many keys should be summarized (Update: I can no longer remember the use case for dicts
  printed via pprint_thing).
• summarization should match numpy [a.a.a ... b b b] not [a a a ...]
• add np.set_printoptions(edgeitems) analogue.

- [ ] options.display.max_seq_items should have a default value != None #3391, #5120 , #5629

via #5753

[cpcloud]

@y-p i can take this if you want

please.