发生IO错误的一些清空操作
This reverts commit 7f839b8790f3e2a5079bc5bba72bad53c8ce04f0.
Added stopOnZero to stop a sound on fadeOut. Added sound.fade property to access the current tween, and sound.fade.ended signal to respond to the end of the fade.
Added stopOnZero, sound.fade and sound.fade.complete callback
Merge remote-tracking branch 'rawSoundAS/master'
创建"optimiBranch"分支, 优化IO加载错误后的处理
添加对单独创建的SoundMananger实例同样可以缓动MasterVolume属性的功能
Merge branch 'optimiBranch' of https://github.com/lynxerzhang/SoundAS into optimiBranch

Conflicts:
	lib/src/treefortress/sound/SoundManager.as
	lib/src/treefortress/sound/SoundTween.as