Consider adding ability to download static resources from remote locations (http, etc) locally for generation of ebook

[develpr]

Sometimes html may contain a resource that is located at a remote location, for example an image hosted on Flickr. It would be convenient to have an option to allow Phindle to automatically download these static resources temporarily for ebook generation.

On the flip side, this may be "too much" and be the responsibility of the developer/user to at least be sure to download these resources locally.