[Feature Request] WebP Support

Hi Frank,
Thanks again for making this awesome plugin. I just have a small thought for AO. Now a days many people are using WebP images in their wordpress site especially with EWWW + Cache Enabler or Optimus + Cache Enabler in this combination.

Now the problem is that Cache enabler do not edit the css or js files instead just handles the output html.

So, I was thinking as AO manages the CSS, if you add an option to change the normal images to WebP version when the page is being viewed from the supported browser like chrome, current firefox beta etc.

Also if the WebP option is selected in Cache enabler then change the images inside the css to the .webp version.

I know this is a huge work in terms of coding, so it’s just a feature request.