vflank 0.6.0

Added

• VCF/BCF input for small variants (vflank small run variants.vcf.gz). The
  input format is auto-detected by extension — no new command or flag. Read
  sites-only; anchor-base REF/ALT is normalised to MAF [Start, End];
  multi-allelic records expand per ALT; symbolic/SV/BND alleles are skipped;
  gene/HGVS come best-effort from a VEP CSQ / SnpEff ANN field. --samples
  doesn't apply to a (sites-only) VCF and is ignored with a warning;
  vflank small inspect previews the normalised variants. New io/vcf.py
  (is_vcf_path, vcf_to_maf_coords, load_vcf); run_small accepts a VCF
  path too. SV-VCF (Delly CT / Manta–GRIDSS BND) remains a follow-up.