Add vep/hgvs endpoint

This endpoint allows users to get VEP results using an HGVS notation
as input. The HGVS can be relative to a genomic position (g), a
transcript (c=coding, n=noncoding), or a protein (p).
change regex to match chrom names with _ or lowercase characters in
allow species with no variation DB to use vep/region endpoint
and another change to allow HGVS fetching to work on species with no var DB
change documentation group
Merge pull request #29 from willmclaren/master

Add vep/hgvs endpoint