将CoreFoudation对象转换成OC对象

例如：

    CFMutableArrayRef ref = CFArrayCreateMutable(kCFAllocatorDefault, 0, NULL);
    NSMutableArray *array = (__bridge_transfer NSMutableArray*)ref;
    [array addObject:@"hello"];
    [array addObject:@"world"];
    NSLog(@"%@",array);