Add support for regions in gene sets

[naegelyd]

Recently there have been requests of along the lines of:

For example, some of these Primary Immunodificiency Pathway genes are not officially genes but regions of known effect and can be millions of bp long so any variant in that region could be suspect.

Without region support, users would need to try to determine all the genes in the region and then add them to the gene list manually. This could be especially tedious for long regions. Supporting a mix of gene names and regions would allow for more flexibility and better support users' needs.

Originally reported as chop-dbhi/varify#350.