Expose Ref<T> type

[elite174]

I suggest to expose Ref from the lib, because it can be useful sometimes to use this type instead of writing ref: T | (element: T) => void

[elite174]

Oh, I've just seen this PR #877

Does it expose Ref type? If so, can it be merged then?

[lxsmnsyc]

I think the new types are going in for the next minor release due to some type changes.