An initial vignette for Variant Annotation.

@siddharthab I also had to do a bit of the refactoring we discussed to make this work.  

The convert-to-BioConductor objects stuff is quick and dirty for now.  It will get better.
are you sure this pseudo code is right?
I was under the impression that the conversion was always (start+1, end) - and that you don't need any clauses here...?