It's better 'retain' returns 'CCObject *' than void

In Objective-C, NSObject's 'retain' returns self.
So I think it's better 'retain' returns 'CCObject *' like 'autorelease'.

In Lua:
local x = CCArray:create():retain()
It's more convenient x is set by CCArray instead of nil.

And added armv7s to valid architecture in xcode project file of CocosDenshion