Developer wiki updates: applying result filters et al.

I finally foundsome time to do some minor updates on the developer wiki. Most interesting change is that I added a page describing how to apply result filters to re-rank search results. This can be done with different features or LSA. See the wiki page here. Filtering of result sets can be easily tried with the current SVN version of LireDemo. I also updated the FAQ a bit including some pointers for those who have their first encounter with Java.