Addresses Issue #58.  Inital commit of refactored code for loading a subset of a biom table.   Draws on biom library code.
Addresses Issue #58.  Inital commit modifying the script to load only the counts corresponding to OTUs that we want to make predictions about.
Adds test code for load_subset_from_biom_str and yield_subset_biom_str.  This currently passes EXCEPT for a case that fails due to incorrect parsing of fields containing commas.  The issue has been raised in the BIOM github project, so I'm leaving it for now, and note what's going on in the comment
Adds a commandline option to suppress the subset loader (for users with high-memory machines, where it might improve runtime on some tables)
Merge pull request #64 from zaneveld/load_subset

Load subset