Add a template for a custom WordPress nav-walker
Add a template for a custom WordPress nav-walker

Previously part of my theme boilerplate (Alhadis/WP-Scratch), this class
has grown less frequently-used over the years, to a point where it's not
even worth including in the boilerplate. The code is still useful though
(albeit in rare scenarios), so it's being retired here instead.

Alhadis/Snippets,Alhadis/Snippets,Alhadis/Snippets,Alhadis/Snippets,Alhadis/Snippets