Implementation of addObserver is incorrect to handle all KVO Options

[RVijay007]

In particular, NSKeyValueObservingOptionInitial will not be triggered correctly as the existing implementation calls addObserver before storing the block, when in fact the block should be saved first as the default addObserver needs to call the block before the method itself even returns.

- (void)addObserver:(NSObject *)observer
         forKeyPath:(NSString *)keyPath
            options:(NSKeyValueObservingOptions)options
            context:(void *)context
          withBlock:(KVOBlock)block
{
    NSMutableDictionary *blocks = objc_getAssociatedObject(self, (void *)[keyPath hash]);
    if (!blocks) {
        blocks = [[NSMutableDictionary alloc] init];
        objc_setAssociatedObject(self, (void *)[keyPath hash], blocks, OBJC_ASSOCIATION_RETAIN);
    }

    blocks[@([observer hash])] = [block copy];
    [self addObserver:self forKeyPath:keyPath options:options context:context];
}