Add a function to detect whether multiple strains of the same species are present in a metagenome sample

[taylorreiter]

Validated with the synthetic metagenome CAMI low [here]() and the real infant gut microbiome time series [here](). The figure below is one of the three things output in a list by this function. It's a plot showing which metagenome samples and which species probably have multiple strains present.