This commit introduces REUSE compliance by annotating all files
with SPDX information and placing the reused licences in the
LICENSES folder.
We additionally removed the docheader tool which is made obsolete
by this change.
The main LICENSE and copyright text of the project is now not under
my personal name anymore, and it belongs to "The Respect Project
Contributors" instead.
This change restores author names to several files, giving the
appropriate attribution for contributions.
When we make changes to the category of a validator, it's easy to forget
to update overall list of validators. This commit a GitHub actions that
will run a console command to check if the documentation it up-to-date.
The job will fail when we need to change the document, but the console
command will fix the issues, so there isn't a lot of friction there.
