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.
There's more value on showing how `assert()` displays the validation
messages than simply showing if `isValid()` returns `true` or `false`.
However, that increases the chances of having outdated documentation, so
I created a doc linter that updates the Markdown files with the
correct message.
We don't often change the tempaltes of validators, but when we do it's
extremely important that the documentation of the validators match the
exact template the validator has.
When we make changes to the code, renaming variables, or adding
parameters to a validator, it's easy to forget to update the
documentation.
With this change, we avoid having a disparity between the documentation
and the code.
