Added ability to pause particle generation for smooth transitions between animation on/off

[admxrd]

Solves #52 -- previously, using destroy would immediately delete all active particles.

Now you can pause onMouseLeave and resume onMouseEnter.

Example:

  const cursor = useRef<CursorEffectResult & PausableResult | null>(null); 
  const dom = <element you want to track>

  React.useEffect(() => {
    if (!dom) return;

    const domElement = dom as Element;
      dom.addEventListener('mouseenter', (e) => {
        if (cursor.current) {
          cursor.current.resume();
          return;
        }
        cursor.current = new emojiCursor();
      })

      dom.addEventListener('mouseleave', (e) => {
        if (cursor.current) {
          cursor.current.pause();
        }
      })
  }, [dom]);