Added classes for chess.

chess/src/chess/Actor.java

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+package chess;
+
+// An actor is an entity capable of making descisions on the board.
+abstract class Actor {
+    ActorColor color;
+}
+
+// The color an Actor may assume.
+enum ActorColor { WHITE, BLACK }

chess/src/chess/Board.java

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+package chess;
+import java.util.Map;
+
+class Board {
+    Map<Coord, Piece> board;
+}
+
+// Measured from top left.
+class Coord {
+    int x, y;
+}

chess/src/chess/Game.java

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+package chess;
+
+class Game {
+    Actor white;
+    Actor black;
+}

chess/src/chess/Piece.java

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+package chess;
+
+// A chess piece.
+abstract class Piece {}
+
+class Pawn extends Piece {}

chess/src/chess/Player.java

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+package chess;
+
+// A human-controlled Actor.
+class Player extends Actor {}