[feat] Add author card to the posts

[rochacbruno]

when

marmite.yaml

  show_author_card: true
  authors:
    rochacbruno:
      name: Bruno Rocha
      avatar: ./media/rochacbruno.png
      bio: I am a person that writes text about things....
      links: [["Fedi", "https://go.rocha.social/@bruno"]]
    jondoe:
      ...    

Then on each post

# Hello
This is the post text

The above, as doesn't specify an author, the first author of the authors list will be assumed and will show on template (default on top) a card showing the information:

(and also on lists but with a smaller size)

This will also require rendering a page author/rochacbruno.html using the group.html template and on that template there will be a list of author Bio and links.

If post has a different author, or even multiple authors then

---
extra:
  authors: ["jondoe"]
---
# Hello
This