Add notebook for filtering

Does NOT use parallel interfaces, so this should probably be updated soon.
However, it does give the general idea.
Add selcet_gamma.py (authored by Amnon)

Used in the filtering notebook.
ignore contested strings
Merge pull request #55 from wasade/ignore_contested_taxstrings

ignore contested strings
Add Amnon's latest select_gamma, plus unit tests
Merge branch 'filtering_notebook' of https://github.com/adamrp/American-Gut
Merge branch 'master' into SummarizeMetaData