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).

Thanks Angie for clarifying this.

It looks like there are two "approaches" for sub-version numbering:
  i-) The "UCSC approach": Having transcript sub-version number (so you don't really need reference sub-version).
  ii-) The "ENSEMBL approach": Having reference sub-versions (so you don't really need transcript version).

Since both approaches are complementary, we just need one of them (either release sub-version or transcript version). Favoring one approach over the other seems "unfair" to me, so I would just propose to make mandatory to have one of them.

So, in a nutshell what I'm proposing is that, for reproducibility reasons we need either:
  i-) A reference sub-version (aka transcript set sub-version)
  ii-) Transcript versions

Does this sound reasonable?