BibTeX output improvements

Here are the 5 changes I made to improve the BibTeX output.

Unfortunately I still haven't found a way to test those, so please review/test before merging.
I managed to get the repl up by setting the :repl-timeout to 5 minutes (!!!), but nevertheless couldn't find how to get BibTeX output for some test data…

If something (either the how or the why) is not clear, please don't hesitate to ask. I might have written very weird code since I'm not at all familiar with Clojure.