Merge pull request #3 from BladeWork/master

The second code from Renfa Feng
Modify files
File changes
Fix three levels errors
Add new sounds(soundtrack, engine, coin, explosion)
Change instructions(add soundtrack, instruction)
Change soundtrack file(KalimbaShort), Add function (get 1 live when player get 1000) to play.ts
add enemyBulletManager and enemyBullet
add enemybullet for playHard.ts, delete function(each 1000 get 1 live)
The logic of try again button? It always starts the easy one.
Change KalimbaShort.wav to mp3
Merge pull request #2 from ZifengX/master

From zif