Rename main branch here or master branch in mono-repo

[mikegerber]

This repo uses a "main" branch while the mono-repo (where this repo is sourced from) uses the "master" branch. While I have no special attachment to either names¹, I do have a special attachment to consistency and propose one of these solutions:

A. The "easy" solution: Rename the branch here to "master"
B. The "laborous" solution: Rename all "master" branches in all projects and the mono-repo to "main"

This consistency is somewhat important because you have to be extra careful to use the proper branch when pushing this stuff to GitHub.

¹ Another thing would be "master-slave" formulation in other contexts, which I do consider inappropriate in a modern age.