Better rendering for faster in-view image display

In previous versions, image only get loaded when the whole image (and not only some part of it) was visible in the viewport. This was not great in terms of UX as the user would have to wait for image to load if the connection is too slow.
Now, the updated rendering logic loads the image as soon as it appears in the viewport.

Also, I'd like to thank @thiamsantos for his help in maintaining the library!