Initial chunk of data for release

The initial chunk of BIOM tables to make available. The READMEs are pretty light so far. This is _not_ ready to merge, the one outstanding aspect is a mention of the sequence level filtering for the AG tables, @adamrp is getting me details momentarily. These are the data that comprised the module 1 release, and will be used for module 2.

The stuff in americangut/util.py is the beginnings of some utility code for the notebooks. Definitely much more to do there.

@ElDeveloper @antgonza if you have a moment, could you please look over this pull request?