Update 5.md

minor modification to improve readability.
Update 6.md

minor modification to improve readability.
Physics Chapter
update physics
Merge pull request #28 from kr15to/patch-8

Update 5.md
Merge pull request #29 from kr15to/patch-9

Update 6.md
Merge pull request #30 from samuele3hu/master

Add content for chapter 11 about `Memory Management` and `Subclass Inherit from c++ Classes Bound to Lua`
Merge pull request #31 from Dhilan007/master

Physics Chapter
Update 13.md

correcion of image's url
remove cocos2d namespace
Merge remote-tracking branch 'refs/remotes/upstream/master'
Merge pull request #32 from MannyDev/patch-4

Update 13.md
Merge pull request #33 from andyque/master

remove cocos2d namespace prefix
continued edits
initial commit
Merge branch 'master' of github.com:chukong/programmers-guide
initial commit
continued edits
edits
resize