download dll and run script art the run time.
http://angryant.com/2010/01/05/downloading-the-hydra/
iOS, Android, Unity3D Education blog,
http://angryant.com/2010/01/05/downloading-the-hydra/
程式写法 http://docs.unity3d.com/Documentation/Manual/AssetBundlesIntro.html 中文,技术解说 http://sky-unity3d.blogspot.com/2013/01/unity-assetbundle.html