Added MK_Stack extension for NSMutableArray.
NSArray+MK_Stack passes tests.
Added interfacefe for MK_Queue.
MK_Queue dequeueObject passes tests.
NSMutableArray+MK_Queue passes tests.
Added MK_firstObject due to support pre iOS 7.
MK_firstObject passes tests.
Fixed pre iOS 7 crash of firstObject.
Merge branch 'release/0.3.3'