Function mutexpect::observed_number_of_mutations

pub fn observed_number_of_mutations(
    mutations: &[PointMutation], 
    indels: &[Indel], 
    seq_annotation: &SeqAnnotation, 
    twobit_ref_seq: &TwoBitFile, 
    filter_plof: bool
) -> Result<HashMap<MutationType, usize>, MutexpectError>