Add stats calculation within the game loop

This patch changes the behavior of the calculation loop of a board
(nextState) to keep track of the changes that happened during the round
(number of cells that died or were born in a given team).

These stats may be accessed by called the getStats() method on a World
instance, which returns a !Stats object:

    const world = Life2.World(...);
    // ...
    const stats = world.getStats();
    displayStats(stats);

Close: https://github.com/nc0fr/life2/issues/8
Signed-off-by: Nicolas Paul <n@nc0.fr>

1 files changed, 1 insertions, 1 deletions

diff --git a/life2/game/index.js b/life2/game/index.js
index b8e8f9c..5d9277e 100644
--- a/life2/game/index.js
+++ b/life2/game/index.js
@@ -25,4 +25,4 @@ export {Board, Grid} from './board';
 export {Cell} from './cell';
 export {Rule, RuleFunction} from './rule';
 export {RulesManager} from './rules_manager';
-export {World} from './world';
+export {Stats, World} from './world';