Add docstrings for merge_lists and merge_dicts.
Add docstrings for merge_lists and merge_dicts.

mozbhearsum/balrog,mozbhearsum/balrog,testbhearsum/balrog,testbhearsum/balrog,testbhearsum/balrog,mozbhearsum/balrog,testbhearsum/balrog,mozbhearsum/balrog