Example code does not work

[adamlwgriffiths]

Running the demo on the README with the latest Pypi release causes an error:

$ python test.py
Traceback (most recent call last):
  File "test.py", line 12, in <module>
    products = client.product.list(order_filter)
AttributeError: 'API' object has no attribute 'product'

The API class does not have a product attribute.