v3.1.0

This release adds the article footer, a place at the end of the article where to insert footnotes, references, acknowledgements, etc. The chosen style takes heavy inspiration from https://distill.pub/, for example, look at the end of this article.

<article>
  ...
  <footer>
    <section>
      <h1>...</h1>
      <p>...</p>
    </section>
    <section>
      ...
    </section>
  </footer>
</article>

• close #63 | add footnotes a3b6f62

v3.0.1...v3.1.0