implements Twin design pattern #63, add credit and rephrase the comments

twin/index.md

@@ -18,3 +18,7 @@ inheritance in java
 
 * to simulate multiple inheritance in a language that does not support this feature.
 * to avoid certain problems of multiple inheritance such as name clashes.
+
+**Credits:**
+
+* [Twin – A Design Pattern for Modeling Multiple Inheritance](http://www.ssw.uni-linz.ac.at/Research/Papers/Moe99/Paper.pdf)

twin/src/main/java/com/iluwatar/twin/App.java

@@ -3,20 +3,12 @@ package com.iluwatar.twin;
 /**
  * Twin pattern is a design pattern which provides a standard solution to simulate multiple
  * inheritance in java.
- * 
  * <p>
- * In this example, there is a ball game, a ball needs to subclass {@link GameItem} which provide
- * some common method like draw and click. Moreover, it needs to subclass {@link Thread} as ball is
- * a moving item (we use {@link Thread} instead of implements {@link Runnable} for example only)
- * <p>
- * Threre is scenario, when user click the ball, the ball will stop, when user click it gain, it
- * will resume to move. We create two class, ons is {@link BallItem} which subclass {@link GameItem}
- * , another is {@link BallThread} which subclass {@link Thread}. These two object both hold a field
- * named "Twin" reference to another object. In {@link BallItem#click()}, it will invoke
- * {@link BallThread} to suspend or resume moving; in {@link BallThread#run()}, it will invoke
- * {@link BallItem} for drawing.
- * 
+ * In this example, the essence of the Twin pattern is the {@link BallItem} class and
+ * {@link BallThread} class represent the twin objects to coordinate with each other(via the twin
+ * reference) like a single class inheriting from {@link GameItem} and {@link Thread}.
  */
+
 public class App {
 
   /**
@@ -44,6 +36,7 @@ public class App {
 
     waiting();
 
+    // exit
     ballThread.stopMe();
   }