tracks reasons for _not_executed
Merge branch 'master' of github.com:biocore/bipy
Merge branch 'master' of github.com:biocore/bipy

Conflicts:
	skbio/core/tests/test_workflow.py
	skbio/core/workflow.py
Merge branch 'master' of github.com:biocore/bipy
removed Grouper as it doesn't look like its in use
Removing workflow commit...
Merge pull request #164 from wasade/grouper_remover

Grouper remover