find_singletons: Find singletons
In surh/HMVAR: Human Microbiome Variant Analysis in R

Finds variants that have singleton alleles and returns the positions and the samples where they ocurr.

1	find_singletons(alleles, midas_dir, info, meta)

`alleles`	site x sample alleles table. Must have column site_id plus one column per sample
`midas_dir`	Instead of alleles table. A path with output files in the format of midas merge can be provided. Must have freqs, depth and info files.
`info`	Optional site info table to append metadata to singleton sites. Must have a site_id column.
`meta`	Optional sample metadata to append to samplew with singleton sites. Must have column sample.