add GameMaster.
Merge pull request #57 from Wu-Hao/master

enabled depth test for all 2d elements,
Merge pull request #58 from Wu-Hao/master

fix AI targeting angle problem
merge with wuhao.
Merge branch 'master' of github.com:fusijie/FantasyWarrior3D
optimize dropblood
merge with fusijie/master
delete invalid code
Merge pull request #59 from zaojiahua/master

optimize dropblood
fix AI bug
Merge branch 'master' of https://github.com/fusijie/FantasyWarrior3D

Conflicts:
	src/Piglet.lua
change knight AI frequency