Soft filter: over-write filter if previously PASS
Soft filter: over-write filter if previously PASS

Supplement for improvements in #30

CuppenResearch/bioruby-vcf,pjotrp/bioruby-vcf,pjotrp/bioruby-vcf,gusevfe/bioruby-vcf,pjotrp/bioruby-vcf,gusevfe/bioruby-vcf,CuppenResearch/bioruby-vcf,gusevfe/bioruby-vcf,CuppenResearch/bioruby-vcf