Otherwise git show fails.

Fix output filter

Closes #6

See merge request !2

Closes #2.

Now whenever a tex file changes a PDF of the latexdiff between
this version and the version of the last successful pipeline for this
branch is made.

Closes #1.

This can be used later to diff things against the last good
commit (e.g. tex files). Also add CI helper scripts to a hidden
directory.

CI_JOB_TOKEN does not give API access (see [1]), so we need to
give projects based on the skeleton some way of accessing the
Gitlab API with at least minimal permissions (so they can
inspect pipelines, other projects etc).

This token needs to be distributed to people with the correct
permissions, who clone this repository. We cannot just store
such a token in the repository itself. Instead we store it
out-of-band in a project snippet that is only accessible to
users with the correct permissions. We use a project snippet
because Gitlab does not yet have group-level snippets (go figure).

[1]:  https://gitlab.com/gitlab-org/gitlab-ce/issues/29566#note_35563221

Sometimes things break if we don't specify this