Rewrite using functional components and hooks about react-scrollama

[maerzhase]

#54 is open.

[maerzhase]

🙈 Created another branch of the rewrite that enables offset defined in pixel values:
https://github.com/maerzhase/react-scrollama/tree/feature/allow-pixel-offset

EDIT:
btw, the functional rewrite that uses relative offset doesn't need a window resize listener because the IntersectionObserver uses relative rootMargin itself. For the the absolute pixel offset we would need to re-incorporate the window resize listener.

[cedricdelpoux]

It's interesting ! Open a PR and we will see