Balance test

[mortonjt]

One thing that could be useful is a very simple command that allows for a balance test.

It would look something like this

1. Bootstrap the samples (via multinomial sampling)
2. Select microbes for numerator / denominator (user specified)
3. Run statistical test and count up the occurrences to calculate CI and pvalues.

Now that microbes can be directly selected from qurro, this should be easier to implement. CC @fedarko

Relevant issue biocore/qurro#222

[mortonjt]

This is the paper worth citing for this : https://www.biorxiv.org/content/10.1101/134536v2