Information-theoretic subset selection

This new feature adds information theoretic subset selection methods for biological data formats using the [PyFEAST](https://github.com/EESI/PyFeast) module. We have a pull request open, but it was closed several months ago. We have made some adjustments to the code and updated the versioning information as well.   
Yes, this needs to be updated to import from [burrito](https://github.com/biocore/burrito) instead of cogent - should just be a change to the import.