Immutable chart state

[djhahe]

Fixes #31

[fenech]

It would be great to get this merged, as it would mean that the library could be used with hooks inside functional components!

function useChart(initialState: IChart): [IChart, typeof actions] {
  const [chart, setChart] = useState(initialState);
  const stateActions = useMemo(
    () =>
      Object.entries(actions).reduce(
        (prev, [key, val]) => ({
          ...prev,
          [key]: (...args: any) => setChart(val(...args))
        }),
        {}
      ) as typeof actions,
    [actions]
  );
  return [chart, stateActions];
}

[marcoalfonso]

Is this pr being merged any time soon?

Have found some bugs on the validateLink function that are caused by this. The link.to property gets wiped when the function is called.