configitems: add `documentation` field
It may be useful to expose documentation information in the help in some form.
This will be populated in a future changeset by using the current comments
that are relevant for users.
# Tests to be disabled when building and testing in the Nix sandbox.
# tests enforcing "/usr/bin/env" shebangs, which are patched for nix
test-run-tests.t
test-check-shbang.t
# doesn't like the extra setlocale warnings emitted by the nix bash wrappers
test-locale.t