WPF实现泡泡龙小游戏效果。
/// -Ball to Ball Collision - Detection and Handling
/// http://stackoverflow.com/questions/345838/ball-to-ball-collision-detection-and-handling
/// -Introduction - The World Of Bouncing Balls:
/// http://www.ntu.edu.sg/home/ehchua/programming/java/J8a_GameIntro-BouncingBalls.html
/// -How to: Render on a Per Frame Interval Using CompositionTarget
/// http://msdn.microsoft.com/en-us/library/ms748838.aspx
/// -The Physics of an Elastic Collision (Part 2):
/// http://www.director-online.com/buildArticle.php?id=532
/// -Elastic collision:
/// http://en.wikipedia.org/wiki/Elastic_collision
/// -Determine where two circles intersect in C#
/// http://blog.csharphelper.com/2010/03/29/determine-where-two-
///https://segmentfault.com/a/1190000012890618
