A How to play page with every rule and a before/after board computed by the
engine, a help button in the header, and the rules in a side panel over the
game page so a game can go on while a rule is looked up.
RULES defines every rule with an example and a lesson; getMoveOutcome works
out a move's effect with the engine, explainMove says what happened, and
describeMove now tells the kind of capture and how many stones it took.
