Add snpEff

[vsatheesh]

Description

TBD

To do

• Add parameters --annotate, --gff, and --vcf
• Write out a design for when a snpEff database exists and for those where there isn't one.
  • Implement a rudimentary call for snpEff when the vcf file is already computed
• Run the pipeline with the minimal data set.
• Update README
• Think about when to release a version

master...feat/snpeff