Feature Request: Add useImmerDraft hook

I rethought this issue #91, and found that this is not general enough. Here I suggest a more general solution that can be applied to arbitrary disjoint union type state and then make us happier with TypeScript + use-immer.

https://github.com/bglgwyng/use-immer/blob/use-immer-draft/src/index.ts I wrote PoC of useImmerDraft, which returns a draft object and its finish.

type Dog = {
  name: string,
  age: number,
};

function SomeComponent() {
  const [dog, updateDog] = useImmerDraft<Dog | null>(null);
  return (
    dog
    ? <button 
         onClick={() => {
           dog.age += 1;
           updateDog(); // no argument!
         }}>
        Increase age! {dog.age}
      </button>
    :  <button onClick={() => updateDog({ name: "John", age: 1 })}>New dog!</button>
  );
}

dog is a draft object. We can get its properties in primitive type and use them in rendering and other logics. The updateDog call without any argument applies the recorded patches and finishes the draft. I think this design is the most type guard friendly one which is possible in TypeScript.

You can use useImmerDraft not only with nullable types but also with arbitrary disjoint union types.

I have a few minor thoughts on it.

Merge useImmerDraft and useImmer into useImmer They have very similar interface, so just add an argument to useImmer and let useImmer serve both roles. function useImmer(initialValue, isDraft = false) And you can select two options with the value of the second argument isDraft. However, I don't have an idea of the proper behavior in the case that isDraft is trueandupdater` is a callback, yet.
If the Draft<S> type bothers the users, then let the type being just S
The name useImmerDraft is not that good. I hope there is a better one.

immerjs / use-immer

Feature Request: Add useImmerDraft hook #92