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).

> So, in a nutshell what I'm proposing is that, for reproducibility reasons we need either: i) reference sub-version; or ii) transcript versions.

Sounds good to me.  Could we call it "i) transcript set version; or ii) transcript versions" though?  I think "reference sub-version" is a broader term -- for example, it could mean reference assembly patch releases like GRCh37.p5 vs GRCh37.p13, that are not necessarily accompanied by annotations, but to which a transcript set could be anchored.  A transcript set version might happen to be the same as the reference sub-version with which it was bundled, or might be independent, e.g. GENCODE V19.