Adds better explosions, shield, and game over

sky/sdk/example/game/lib/action.dart

Index: sky/sdk/example/game/lib/action.dart
diff --git a/sky/sdk/example/game/lib/action.dart b/sky/sdk/example/game/lib/action.dart
index f0763c02c01bd09d23b335c1f60d7455d95d6dbd..70c25bf12d2bef41c2ac6d2dda57390db396d641 100644
--- a/sky/sdk/example/game/lib/action.dart
+++ b/sky/sdk/example/game/lib/action.dart
@@ -1,6 +1,6 @@
 part of sprites;
 
-typedef void PointSetter(Point point);
+typedef void ActionCallback();
 
 abstract class Action {
   bool _finished = false;
@@ -123,7 +123,7 @@ abstract class ActionInstant extends Action {
 }
 
 class ActionCallFunction extends ActionInstant {
-  Function _function;
+  ActionCallback _function;
 
   ActionCallFunction(this._function);
 
@@ -132,10 +132,10 @@ class ActionCallFunction extends ActionInstant {
   }
 }
 
-class ActionRemoveFromParent extends ActionInstant {
+class ActionRemoveNode extends ActionInstant {
   Node _node;
 
-  ActionRemoveFromParent(this._node);
+  ActionRemoveNode(this._node);
 
   void fire() {
     _node.removeFromParent();