Redux-Saga api calls

Hi @epeli!

I was wondering how you implement Redux-Saga API calls.

If I take the default Redux-Saga readme example:

```
import { call, put, takeEvery, takeLatest } from 'redux-saga/effects'
import Api from '...'

// worker Saga: will be fired on USER_FETCH_REQUESTED actions
function* fetchUser(action) {
try {
const user = yield call(Api.fetchUser, action.payload.userId);
yield put({type: "USER_FETCH_SUCCEEDED", user: user});
} catch (e) {
yield put({type: "USER_FETCH_FAILED", message: e.message});
}
}

/*
Starts fetchUser on each dispatched `USER_FETCH_REQUESTED` action.
Allows concurrent fetches of user.
*/
function* mySaga() {
yield takeEvery("USER_FETCH_REQUESTED", fetchUser);
}
```

The pattern is to dispatch an action (`USER_FETCH_REQUESTED` ) and handle it in the saga. The saga calls the API and puts the result to either `USER_FETCH_SUCCEEDED` or `USER_FETCH_FAILED`.

Now when modeling this in immer-reducer would I get the following?
- an empty method called `UserFetchRequested`
- a method called `UserFetchSucceeded` which would update the draft
- a method called `UserFetchFailed` which would update the draft

Seems kinda weird... especially the empty method just for creating an action.

Would love to hear your view on this.

Thanks,

Michel