The following two are optional. If both are defined, then the script will download avatars and will not use hotlinks.
1. (lua) `pleroma_avatar_path` = (yaml) `pleroma-avatar-path`: a string ending in `/`, the folder containing avatars as referenced by the web page (e.g `<img src="(pleroma-avatar-path)/avatar.png"/>`).
2. (lua) `pleroma_avatar_save_path` = (yaml) `pleroma-avatar-save-path`: a string ending in `/`, the folder in which avatars are downloaded to.
If multiple pages will be storing avatars in the same folder, create `config.lua` and assign the variables there. If a specific page will have its own directory for images, assign the variables in the manuscript's YAML header.
The filter exports variables that can be used in a Pandoc template.