Import gambit-13.1.0 as wip/gambit.

Gambit is a library of game theory software and tools for
the construction and analysis of finite extensive and strategic games
Update to 0.2.3.2

changes:
0.2.3.2
  - D.H.Strict: only evaluate values if used
      Before this change all value arguments would be evaluated to WHNF even
      if they were never inserted into the map.
      Fixes https://github.com/tibbe/unordered-containers/pull/69
      Fixes https://github.com/tibbe/unordered-containers/issues/57
      Also fix a strictness bug in fromList (fixes https://github.com/tibbe/unordered-containers/pull/61).