Used dispatch_once_t for NSDateFormatter creation in order to avoid crashes when multiple threads use KZPropertyMapper.
Merge pull request #36 from Eddpt/fix/date-formatter-initialization

Used dispatch_once_t for NSDateFormatter creation
Merge pull request #34 from marekcirkos/master

Unified assert behaviour while error handling
Fixed Warning related to casting converting void pointer and function pointer

Assigning a void pointer to a function pointer is an undefined behaviour.
If more strict warnings are enabled and warnings are treated as errors, this can prevent the project from compiling.
Merge pull request #38 from iOSCowboy/master

Fixed Warning related to casting converting void pointer and function pointer