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 have a question about that: We want these records sorted ("more important scores" first, let's ignore the definition of what "more important" means for the moment).

I created an object "GAScores" where I wanted to specify the order (since it will be used in other entries). 
Do you prefer to use "array<GAScores>" and add a comment on how these should be sorted? What's the best approach?