Support generation of LaTeX files without JOSS styling

[tarleb]

A new output format arxiv is added, which will generate a LaTeX file
paper.arxiv that has no JOSS logos and no metadata sidebar. However,
the general styling is retained.

[tarleb]

After reading the arXiv submission guidelines, I conclude that the following problems should be fixed:

• It must be possible to process the resulting file with pdflatex; we currently use lualatex, and the template is tuned for that.
• Optional: generate a .bib file that contains all references used in the paper, but only those. It seems that this file is not used, by arxiv, and we're using citeproc instead of bibtex, but it could be helpful.

[arfon]

It must be possible to process the resulting file with pdflatex; we currently use lualatex, and the template is tuned for that.

Does that mean this approach is fundamentally flawed or just that there is some more work to do?

[tarleb]

Ah sorry, I forgot to close this. The PR has been superseded by the recent "preprint" format changes: The LaTeX generated there is very close to pandoc's default template, so it doesn't have these issues.