Fixes for missing years and unknown entry types

Hi, I intend to use your excellent tool for my website. However, it had trouble with some of my bibtex entries – no output at all was produced when a year was missing, or when a publication type was used that is allowed by the BibTex Parser, but does not have its own bib2html handler.

I have fixed this by setting the year to 'To Appear' if missing, and falling back on 'misc' if there is no dedicated handler. I have also modified the example.html file slightly so that you have something to check this against.