Add extended filtering options.

We use this functionality for filtering the bibtex file according to the keywords in the bibtex entries. In order to allow the visitor narrowing the list of publication to specific research topics. If you like the basic idea I can refine the push request incorporating your feedback. 

The bibentries in the bibtex file are filtered according to the entry specified after "select" option. For example, "select=year". The dropdown menu is filled with the entries specified after option "allow" separated with commas. For example,
allow="2011, 2012", which means we select between these two years.