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.   
Can these data be placed into qiime_test_data, and can the usage example be updated to reflect the appropriate structure? Basically, file paths need to be prefixed with `$PWD`