Add module to convert codemeta documents to bibtex entries

@rdicosmo I am not familiar with BibTeX; could you look at the tests and check the generated BibTeX entries make sense?

test_licenses in particular, as https://gitlab.inria.fr/gt-sw-citation/bibtex-sw-entry/-/blob/master/biblatex/software-biblatex.pdf mentions it can be a list but not how to format it.