explore: Find unknown recombinants in dataset

[ktmeaton]

A current limitation in rebar is that you somewhat need to known which populations in the dataset are recombinants. I'd like to write a new subcommand maybe explore that will check all pairwise combinations in a dataset.

So it would work like: rebar explore --dataset-dir dataset/sars-cov-2 --output-dir output/explore/sars-cov-2.

And you could supply the --min-parents/--max-parents arguments like in rebar run. If --min-parents 2 and --max-parents 2, rebar would compare every population against every other pairwise combination. It would be a pretty hefty calculation, but could be a good assessment for Issue #1 (efficiency improvements).