In contrast to the existing -D option, it would be a simple machine-readable output; and given a document such as en/reference, it would list its subdocuments.

Using this output we can reimplement the parallel build of all documents (AllBuilder._wrapper) using a simple Makefile.

CC: @jhpalmieri

Component: documentation

Author: John Palmieri

Branch/Commit: b67798e

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/31353