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).

this should really go next to GAPosition in common.avdl and be shared almost all of our files. 
we have these same 3 fields in many several places

note: separate pr, not your burden :)