新增box复合体 修复vector2运算问题

demo/src/game/VerletDemo.ts

@@ -0,0 +1,27 @@
+class VerletDemo extends RenderableComponent {
+    private _world: VerletWorld;
+
+    protected getWidth(){
+        return 800;
+    }
+
+    protected getHeight(){
+        return 600;
+    }
+
+    public onAddedToEntity(){
+        this._world = new VerletWorld(new Rectangle(0, 0, 800, 600));
+
+        this._world.addComposite(new Box(new Vector2(100, 100), 50, 20));
+        this._world.addComposite(new Box(new Vector2(10, 10), 200, 100));
+        this._world.debugRender(this.entity.scene.stage);
+    }
+
+    public update(){
+        this._world.update();
+    }
+
+    initialize() {
+    }
+
+}