Reference Issue

Fixes#863

What does this implement/fix? Explain your changes.

Whenoutput_dict=True andtarget_names is given, set the keys of theoutput_dict to the correspondingtarget_names

{'label 1': {'pre':0.5,             'rec':1.0,             ...            }, 'label 2': { ... },  ...}

Whenoutput_dict=True andtarget_names is not given, set the keys of theoutput_dict to the corresponding labels instr format

{'0': {'pre':0.5,             'rec':1.0,             ...            }, '1': { ... },  ...}

Any other comments?