Add support for biblatex's "addbibresource" command, which requires bib files with extensions.

Add addbibresource to commands.
Create a simple check so that a second file extension is never added to the bib filename.
Change id of BibLaTeX translator to that of the official translator which is now included in the repository.
Merge pull request #14 from andersjohansson/enhanced-biblatex

Enhanced biblatex