Few things

partial transition to biom 2.0, and su

* support for unique over a column hosts (ie, don't count multiple times for the same host_subject_id)
* use biom_open
* filterSamples -> filter
just a note, this change reqs BIOM >= 2.0. It is possible the rest of the code base is not in full compliance with 2.0, but I think I got everything