resolve_image_path(
href,base_path,image_resolver,hide_images) ->abs_path
Resolve an image href to a renderable PNG path, or return nil
Local hrefs are resolved against base_path and must point to an existing
PNG file. Schemed hrefs (http://…, wiki:…, media:…) are delegated
to the image_resolver callback when one is provided. The hide_images
flag short-circuits everything.