Add missing docstrings for identifiers functions
Add missing docstrings for identifiers functions

sorgerlab/indra,sorgerlab/indra,sorgerlab/belpy,johnbachman/indra,johnbachman/indra,johnbachman/belpy,sorgerlab/belpy,bgyori/indra,johnbachman/belpy,sorgerlab/belpy,bgyori/indra,johnbachman/belpy,sorgerlab/indra,bgyori/indra,johnbachman/indra