Put shell sounds to their own directory.

1. 二进制
     assets/sfx/weapons/shell-12gauge1/var0.wav
2. 二进制
     assets/sfx/weapons/shell-12gauge1/var1.wav
3. 二进制
     assets/sfx/weapons/shell-12gauge1/var2.wav
4. +0

   -0
     assets/sfx/weapons/shells/12gauge/var0.wav
5. +0

   -0
     assets/sfx/weapons/shells/12gauge/var1.wav
6. +0

   -0
     assets/sfx/weapons/shells/12gauge/var2.wav
7. +0

   -0
     assets/sfx/weapons/shells/5-56/var0.wav
8. +0

   -0
     assets/sfx/weapons/shells/5-56/var1.wav
9. +0

   -0
     assets/sfx/weapons/shells/5-56/var2.wav
10. +0

    -0
      assets/sfx/weapons/shells/7-62/var0.wav
11. +0

    -0
      assets/sfx/weapons/shells/7-62/var1.wav
12. +0

    -0
      assets/sfx/weapons/shells/7-62/var2.wav
13. +0

    -0
      assets/sfx/weapons/shells/9mm/var0.wav
14. +0

    -0
      assets/sfx/weapons/shells/9mm/var1.wav
15. +0

    -0
      assets/sfx/weapons/shells/9mm/var2.wav
16. +0

    -0
      assets/sfx/weapons/shells/hk40/var0.mp3
17. +0

    -0
      assets/sfx/weapons/shells/hk40/var1.mp3
18. +0

    -0
      assets/sfx/weapons/shells/hk40/var2.mp3