message: feat: Support `:categories` in permalink
diff: @@ -12,6 +12,7 @@ use jsonfeed;
  use jsonfeed::Item;
  use jsonfeed::Content;
  use serde_yaml;
  +use itertools;
  #[cfg(all(feature="syntax-highlight", not(windows)))]
  use syntax_highlight::{initialize_codeblock, decorate_markdown};
  @@ -98,6 +99,9 @@ fn permalink_attributes(front: &frontmatter::Frontmatter,
  attributes.insert(":slug".to_owned(), front.slug.clone());
  + attributes.insert(":categories".to_owned(),
  + itertools::join(front.categories.iter(), "/"));
  +
  attributes.insert(":output_ext".to_owned(), ".html".to_owned());
  if let Some(ref date) = front.published_date {
  