refactor classes in game.dart to separate files

lib/game/embedded_game_widget.dart

@@ -0,0 +1,38 @@
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart' hide WidgetBuilder;
+
+import '../position.dart';
+
+import 'game_render_box.dart';
+import 'game.dart';
+
+/// This a widget to embed a game inside the Widget tree. You can use it in pair with [SimpleGame] or any other more complex [Game], as desired.
+///
+/// It handles for you positioning, size constraints and other factors that arise when your game is embedded within the component tree.
+/// Provided it with a [Game] instance for your game and the optional size of the widget.
+/// Creating this without a fixed size might mess up how other components are rendered with relation to this one in the tree.
+/// You can bind Gesture Recognizers immediately around this to add controls to your widgets, with easy coordinate conversions.
+class EmbeddedGameWidget extends LeafRenderObjectWidget {
+  final Game game;
+  final Position size;
+
+  EmbeddedGameWidget(this.game, {this.size});
+
+  @override
+  RenderBox createRenderObject(BuildContext context) {
+    return RenderConstrainedBox(
+        child: GameRenderBox(context, game),
+        additionalConstraints:
+        BoxConstraints.expand(width: size?.x, height: size?.y));
+  }
+
+  @override
+  void updateRenderObject(
+      BuildContext context, RenderConstrainedBox renderBox) {
+    renderBox
+      ..child = GameRenderBox(context, game)
+      ..additionalConstraints =
+      BoxConstraints.expand(width: size?.x, height: size?.y);
+  }
+}
+