Stop component re-rendering with useSelector

[GeraldHost]

As per this ticket: #18

I've tested this solution and it seems to fix the problem with the re-renders.

[RichardLindhout]

Hey very cool PR, I forgot about it:
Will this still work:
#13

BTW esm build etc are very nice

[GeraldHost]

@RichardLindhout let me check, I also just realised I'm committing the build which is not ideal so will sort that too.

[gaberogan]

Looks like it's not initialized properly. Recommend updating this useState(() => selector(v)); and making a new PR since the code has divergged.

  function useSelector(selector, comparator = equ) {
    const [state, setState] = useState(() => selector(v));
    subscribe(() => {
      const selectedValue = selector(v);
      if (!comparator(selectedValue, state)) setState(selectedValue);
    });
    return state;
  }