-p should allow to select VCF files (both normal and zipped)

[nevrome]

Currently the command line documentation for -p explicitly excludes VCF files with For VCF please see option --vcfFile.

I see no reason for this restriction. -p should support reading of .vcf and .vcf.gz just as --vcfFile as a convencience feature.

[stschiff]

I have zero emotions here, that's fine. Generally I prefer the "there is exactly one way to do something" philosophy, both for teachability and maintenance, but if that's something that people want. No problem.

[stschiff]

This was promptly addressed in #318