Improve formatting of multiple authors in bib completion

This  fixes [#149](https://github.com/LaTeX-Box-Team/LaTeX-Box/issues/149): when there are three or more authors the bib completion window will display " 'surname of the first author'  et al." Please review the pull request because i) I think I've mixed spaces and tabs when indenting and ii) I'm not quite sure about the regex I used to get the first author before the comma.  
Thanks!