Add support for native lazy loading

[coliff]

I'd love to see support for native lazy-loading of images. I would imagine if it detected support for native lazy loading it would add loading="lazy" to images and if not supported then the plugin would work as usual (with JavaScript)
REF: https://addyosmani.com/blog/lazy-loading/

[jumedeenkhan]

This feature will be included in the next update of the plugin.