Find Distance Calculation in source code from Sankaran Lab

There are two main papers that we are trying to emulate. Each of them must have used a specific distance calculation to determine the difference between two mitochondrial sequences.

Please look through the code on their github repo and find the section that performs the calculation.

Ludwig et al., Cell, 2019. ([Vijay Sankaran Lab](https://www.bloodgenes.org/) & [Aviv Regev Lab](https://www.broadinstitute.org/regev-lab), Broad Institute) "Lineage Tracing in Humans Enabled by Mitochondrial Mutations and Single-Cell Genomics." [paper](https://sci-hub.tw/10.1016/j.cell.2019.01.022), [github repo](https://github.com/sankaranlab/mito-genotyping)