Add documentation for NSDictionary+Safety

Signed-off-by: Jai Govindani <govindani@gmail.com>
Add documentation for NSMutableArray+Safety

Signed-off-by: Jai Govindani <govindani@gmail.com>
Add documentation for NSMutableDictionary+Safety

Signed-off-by: Jai Govindani <govindani@gmail.com>