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
This seems a bit hackish, but it removes a level from the potential `if` chain and is a fairly explicit solution, which I think is valuable. I would probably rename the class to `_AllTrue` however as it isn't really a public member of `mapping.py` just an internal utility class.