IE9 IE10 support?

[TremayneChrist]

This is here to gather feedback on the need for this. Please comment below 👇

[vipcxj]

If this library support ie 9/10, I will change resize-observer-polyfill to this library.

[TremayneChrist]

Tested working when these fixes are implemented 🎉

Unsupported Feature	Introduced	Fix for IE9+
Map	IE11	Polyfill the map API internally, or, request that a Map polyfill is included.
MutationObserver	IE11	Fallback to MutationEvents.
requestAnimationFrame	IE10	Fallback to setTimeout.

[TremayneChrist]

I may put a draft of this together, but I'm worried about bloating the bundle too much. Will have a think about some options.

[TremayneChrist]

To support IE9/10, using v3.2.0 and above, you'll need to include these additional polyfills:

Additional Polyfill	Required for
WeakMap	IE9, IE10
MutationObserver	IE9, IE10
devicePixelRatio	IE9, IE10
requestAnimationFrame	IE9

I'll move this information to the readme at some point.

[TremayneChrist]

Will also add improvements so that devicePixelRatio and requestAnimationFrame are not required.