hexdoc.data.sitemap.delete_updated_books assumes a file structure like .../{version}/{lang}/.sitemap-marker.json instead of using ModPluginWithBook

[object-Object]

Ideally, ModPluginWithBook should have a method to get the relative path from a site book path (eg. /v/1.0.0/1.0/en_us/) to the site path (eg. /v/1.0.0/1.0/). This should be tested for the case where these paths are the same.

[object-Object]

This would also be helpful for the new image rendering, to get a shorter path to the renders directory (eg. ../../../../v/1.0.0/1.0/renders/... vs ../renders/...).