Average pooling

def avg_pooling(attrs, inputs, proto_obj):
    """ Average pooling"""
    new_attrs = translation_utils._fix_attribute_names(attrs,
                                                       {'kernel_shape': 'kernel',
                                                        'strides': 'stride',
                                                        'pads': 'pad',
                                                       })
    new_attrs = translation_utils._add_extra_attributes(new_attrs,
                                                        {'pooling_convention': 'valid'
                                                        })
    new_op = translation_utils._fix_pooling('avg', inputs, new_attrs)

    return new_op, new_attrs, inputs