v1.0.0

Added

• Observer component
• threshold prop to Lazy and LazyGroup
• viewport prop to Lazy and LazyGroup which works like root of IntersectionObserver

Changed

• cushion prop works now like marginRoot of IntersectionObserver
• jsOnly prop is now clientOnly
• Viewport detection to use IntersectionObserver API with code heavily based on
  @researchgate/react-intersection-observer
• LazyGroup no longer extends from Lazy as both use Observer now
• onViewport receives intersection observer event as first parameter

Removed

• checkElementsInViewport

Fixed

• Production build no longer requires PropTypes