[Bug/Feature Request] Resize Event Listener not appropriate when container option not window

[haxxxton]

Currently VirtualList attaches to the 'resize' event on the supplied container option.

This is fine when window is supplied as the container, but will not fire when an alternate element is supplied.

There are a number of approaches for detecting element size change of non-window elements that could be integrated to correctly trigger this.refreshState.

Happy to submit a PR if you wanted to choose which lib you liked best.

[developerdizzle]

Personally, I think the ResizeObserver pattern with a note about requiring a polyfill would be best.