Support inner dict combination

[takelushi]

examples/dict_params.py is comprex.

d = {
    'a': combu.create_values([1,2,3]),
    'b': combu.create_values([1,2,3])
}
params = {
    'v': [1,2,3],
    'd': d
}

To

params = {
    'v': [1,2,3],
    'd': {
        'a': [1,2,3],
        'b': [1,2,3]
    }
}