增加弹幕绘制缓存功能
修复一些弹幕缓存产生的bug
changed a method name of danmakusurfaceview
deleted multi drawing task class
rename CacheManagerDrawTask class
Removed some debug logging code
修复退出可能造成的fc问题
solved a fc problem caused by thread exits
added object pool to reduce new object times
solved seeking error
fixed Some synchronization bugs
removed debug codes
updated README.md
Merge pull request #2 from ctiao/master

update