- update references to default branch name in docs, workflows
- use HEAD in github urls, which always works regardless of default branch name
- fix petstore URLs since the old petstore links seem to have stopped working
- Using the new template_vars setting (#1872), allow the variable
`announcement` to create a header message on all the pages in the
title, or the variables `announcement_{home,login,logout,spawn}` to
set variables on these single pages.
- This is not the most powerful method of putting an announcement into
the templates, because it requires a server restart to change. But
the invasiveness is very low, and allows minimal message
without having to touch the templates themselves.
- Closes: #1836
