Biocaml_unix.BamstatsSourcetype t = {total : int;qc_pass : int;not_passing_quality_controls returns false, assumed for all other counts
single_reads : int;has_multiple_segments returns false
read_pairs : int;has_multiple_segments and first_segment
mapped_reads : int;!segment_unmapped and !secondary_alignment and !supplementary_alignment
mapped_pairs : int;has_multiple_segments and first_segment and each_segment_properly_aligned and !secondary_alignment and !supplementary_alignment
}