Vcf symlink

This is a pretty junky script for Operations and/or data-transfer to symlink a bunch of build's SNV and Indel files. It is unclear to me how to test this so the test case is just a use of the module.
Hopefully `sanitize_string_for_filesystem` does its job, but it may be good to revise these comments.  (I'd remove "I think" where it appears.  If there's uncertainty hopefully we can resolve it here in this PR!)