Cosmetic changes, Biblatex style, improved pdf linking

Hi,

I made some changes to the script, I think they are not too specific, except for the fact that I switched from the bibtex norm to the biblatex one (on the whole, things are better defined than with bibtex, but it is not always compatible with old bib files…).

I also added the support for the File field from JabRef to link pdfs.

And I updated the README file.

If needed I can try to cut this pull request in multiple ones…