make FTKeepFilter sample specific
set filter to pass if we do not have a bam readcount entry for the sample
make sure the NCallersFilter handles valid_callers that aren't in the VCF
refactor for clarity
pass alleles with VAF of 0
we should set the VAF to 0 if the coverage is 0, irregardless of readcount
only interpret ft string for alt alleles that were called in the sample
add missing passed_alt_allele param to interpret_entry subroutines
make default value an array ref for consistency, add test coverage
keep positions with readcount and/or coverage of 0
add correct handling of nonexisting readcount entry, vaf of 0. Add test coverage
add errno to the die message so we can se why it failed