Short title and short author for beamer slides

[raffaem]

Describe your proposed improvement and the problem it solves.

Suppose you have:

---
title: "The Princess Bride: S. Morgenstern's Classic Tale of True Love and High Adventure"
author: "Author 1, Author 2, Author 3, Author 4"
institute: "My Institute"
theme: Madrid
date: \today
toc: true
---

# Section 1

## Slide 1

Lorem ipsum

An you compile it with:

pandoc --from markdown --to beamer --output main.pdf pres.md 

In the footer you obtain:

With author and title going off the boundaries.

beamer allows you to insert short title, short author and short institute, for instance \title[short title]{Long title}.

See page 92 of beamer guide.

I then propose a field short-author , short-title and short-institute in the YAML.

See:

https://stackoverflow.com/questions/50225802/r-markdown-pandoc-beamer-presentation-with-short-title?noredirect=1
quarto-dev/quarto-cli#5620
https://www.reddit.com/r/quarto/comments/1by9i1a/how_to_set_a_shorttitle_and_shortauthor_for_a/