Removed duplicate code that existed inside and outside of get*Link() functions.
Added option BIBTEXBROWSER_LINKS_IN_NEW_WINDOW. It is used instead of BIBTEXBROWSER_BIB_IN_NEW_WINDOW for external links (everything but [bibtex]).
The sorting mechanism relied solely on strcmp before, which yielded a more or less random result.
It is now possible to define an order as long as the strings in the bibtex file are given in their standard English form.
In output though, the strings are internationalised.