Split `model` according to the layers in `splits`.

def split_model(model:nn.Module=None, splits:Collection[Union[nn.Module,ModuleList]]=None):
    "Split `model` according to the layers in `splits`."
    splits = listify(splits)
    if isinstance(splits[0], nn.Module):
        layers = flatten_model(model)
        idxs = [layers.index(first_layer(s)) for s in splits]
        return split_model_idx(model, idxs)
    return [nn.Sequential(*s) for s in splits]