Feature: Variant annotations


Hi everyone,
  This is a pull request for adding an Avro IDL file for variant annotations (annotations.avdl). 
  Annotations include records for variant effect, impact, coding and non-coding information, 
clinical relevance, etc.
  It is heavily based on VEP (ENSEMBL's Variant Effect Predictor) and SnpEff (an annotations 
tool I wrote).

I agree that {1,2,3,...., 42} is more difficult to interpret - but {0, .5,..., 1} isn't. 

If the space is well defined from 0 to 1, then moderate immediately becomes .5 in any analysis that uses 3 buckets. And sorting by impact becomes very simple, and we never have to haggle about new enums and where they fit in :)