Merge pull request #14 from yuye-liu/master

Enemy logical
added sound effect to missile explosion, updated the ground texture
Merge branch 'master' of https://github.com/Wu-Hao/Moon3D

Conflicts:
	Classes/GameLayer.cpp
updated ground texture
vect modify
Merge branch 'master' of https://github.com/Wu-Hao/Moon3D
merge