Add "CheatBot" (avg score 24.34).

CheatBot does what its name implies: it uses global variables to
transfer information between the players. This means that every
player automatically knows (thanks to pleaseObserveBeforeMove())
the entire contents of his own hand at all times.

It's still very hard to come up with a strategy for getting the
best possible average score!
Improve CheatBot (avg score 24.50).

CheatBot now tries to enable followup plays from its partners;
for example, if Alice has the blue 1 and the red 2, and Bob has
the red 3, Alice will prefer to play the red 2 even though the
blue 1 is "lower" (assuming that Bob doesn't also have the blue 2).

Also, make the "temporize early just to see what comes up" heuristic
a little more continuous. It's still not a great heuristic, in that
it's hard to explain rationally why this exact heuristic should help;
but it does boost the average score by a few hundredths of a point.
More work is needed.
Add a preliminary "FinesseBot" (avg score 18.94).

Right now, FinesseBot doesn't live up to its name; it's just a copy
of ValueBot with an additional pass at the start of every turn to
update handKnowledge_ with deductions based on the currently public
knowledge. This still boosts its average score by about 0.4 ppg.
Rename FinesseBot to HolmesBot. Improve its average from 18.9 to 19.2.

"HolmesBot" is a much better name for a bot that makes use of deductive
reasoning, and that's the main way this bot differs from ValueBot.
It now keeps track not only of the publicly visible played/discarded cards,
but also of the cards that have been definitely identified in other
players' hands. So, for example, if one red 3 is in the discard pile
and the other is in Bob's hand, Alice can conclude that her 3 is
definitely not red (and this may later allow her to deduce that
whatever color her 3 may be, it is definitely playable).

Ultimately I'll want to switch over to an exhaustive search like
Dancing Links, rather than this cascade of ad-hoc deductive rules.
But for now it's pretty good.
Remove unused variables from HanabiServer.

No change in behavior.