Add Immer functionality

[BigAB]

Simple is better.

Having to write non mutating code can become tedious:

const item = state.find(item => item.id === payload.id);
const index = state.indexOf(item);
return [...state.slice(0, index), { ...item, selected: true }, ...state.slice(index + 1)]'

better to just pass an immer draft object and let the user mutate it, but still give immutable state updates.

const item = state.find(item => item.id === payload.id);
item.selected = true;
return state;