Transient menu for `a2ps` to print text files fancy-like

Inspired by [lp-transient](https://www.reddit.com/r/emacs/comments/wg7pq9/a_transient_menu_for_lp_for_easier_printing_from/), I've written something similar for the `a2ps` program: [a2ps-transient](https://git.sr.ht/~swflint/a2ps-transient)