Last patch I've posted implements "strict ordering rule" on key sharing dict.

* Insertion order should be strictly equal to order in shared key.
  If insertion position is not equal to ma_used, convert it to combined
  form.

* Deleting from split table is prohibited.  Convert the table to combined form.  (to keep ma_used == next insertion position rule).


I ran sphinx-build on this patch and master branch.
("intern" in the result is incomplete implementation of my new idea.
 Please ignore it in this issue.)

https://gist.github.com/methane/df89221222cc2474af1fe61a960e100d

Summary
-------------
Speed:  No regression from master branch.
Memory usage:  Reduced from 172452k to 160876k