message: feat(page): page.file.parent variable
  This can be used for referencing assets in the folder the file came
  from.
  Fixes
diff: @@ -137,8 +137,10 @@ fn document_attributes(front: &cobalt_model::Frontmatter,
  // Reason for `file`:
  // - Allow access to assets in the original location
  // - Ease linking back to page's source
  - let file: liquid::Object = vec![("permalink".to_owned(),
  - liquid::Value::str(source_file.to_str().unwrap_or("")))]
  + let file: liquid::Object =
  + vec![("permalink".to_owned(), liquid::Value::str(source_file.to_str().unwrap_or(""))),
  + ("parent".to_owned(),
  + liquid::Value::str(source_file.parent().and_then(Path::to_str).unwrap_or("")))]
  .into_iter()
  .collect();
  let attributes =
  