handle user input errors more gracefully

[toejough]

as in, if the user forgets to pass a list of arguments in their test (data_driven(['foo'], {'first': foo}) instead of data_driven(['foo'], {'first': [foo]})), we should give them a better error than:

File ".../lib/python3.5/site-packages/dado/dado.py", line 63, in dd_decorator
    new_test, new_name = build_test(test, suffix, names, args)
  File ".../lib/python3.5/site-packages/dado/dado.py", line 50, in build_test
    kwargs = {k: v for k, v in zip(arg_names, args)}
TypeError: zip argument #2 must support iteration