resize event support

[jihgao]

Currently, it does not support resize event which causes some of the images would not be loaded if the window size changed. Could someone look into it?

[s0kil]

@jihgao This library was created to be minimal, you could read more @ https://toddmotto.com/echo-js-simple-javascript-image-lazy-loading/

But echo does have a render function for cases like this. @ https://github.com/toddmotto/echo#render

Creating a performant onresize event.
https://iamakulov.com/notes/resize-scroll
https://codepen.io/bencentra/pen/PwapWX