Feature request: VCF output

[pettyalex]

My group still works with many tools that cannot read in BCF and need .vcf.gz still.

Would it be possible to allow outputting VCF? It seems like right now, the only reason that we cannot output VCF is because of bugs in xcftools, specifically because odelaneau/xcftools@394bbaf is not released in 5.1.1 and there's a similar bug with the line

		} else if (hts_fname.size() > 5 && hts_fname.substr(hts_fname.size()-5) == "vcf.gz") {

because ".vcf.gz" is 6 characters, not 5.

Thoughts on VCF output?