Re-work PureDoubleChow.

Use collections.Counter insteda of nested for loops. Also use the
start tiles only, and take into account that one of them may be open
(the last meld on ron.)
Twice pure double chow.
Quick fix

This problem may be an effect of this being based on the 4.11 branch
*and* the master branch.
Make iterating over a single rule (that is not None) work by passing
it as a one-element list.
Remove a comment. That bit now has its own ruleset.
Code for Japanese scoring, incomplete.
Split the seven pairs rule so we can change the fan and the fu values.
Call mangan the limit and make it editable.
Hide some options (roof off/kong box size).
Comment on how the 'no other points' should be handled.
Use the limits_limit to deal with the no double yakuman, but Four big winds is double yakuman issue. N.B.: Breaks without the next (!) commit.
Japanese style calculation of one hands point.
The limits_limit parameter in Rule and Score to deal with the curious “no double yakuman, but Four Big Winds is yakuman” situation.
The Japanese point calculation code does not belong in game. It is now
in rule.Score.
Merge branch 'feature-japanese-style-scoring' into feature-riichi