implement dynamic mismatch filter for long reads based on read length

[colindaven]

see suggestions from samtools/samtools#1789

# works with samtools 1.16.1 - must upgrade samtools from 1.11

samtools view -e '[NM]/length(seq) < 0.1' test.sorted.bam | wc -l
7
samtools view -e '[NM]/length(seq) < 0.2' test.sorted.bam | wc -l
12