improves the configurability of the output through CSS classes (adds .bibmenu and .bibanchor)
preserves math formula for use with MathJax (bug reported by Elvis)
fixes a bug in Javascript progressive enhancement (bug reported by Elvis)
improves the configurability of the output through CSS classes (adds .bibcomment)
improves the configurability of the link menu ([bib], [pdf], ...)
adds support for "file" fields (exported by Zotero)

suggested by Luis J. Villanueva, see https://github.com/monperrus/bibtexbrowser/pull/14
adds a link to the github page
prevent collision if i18n function already exists
Merge pull request #20 from tbrisker/master

prevent collision if i18n function already exists
Merge pull request #4 from monperrus/master

Rebased