Fixing some inconsistent documentation in README.md such that it correctly reflects the current nature of the python client.

Hello!

Thank you for publishing this preview of this exciting new technology!  I could not wait to start playing with it :D

While using the python client that is on the current master branch, I experienced an inconsistency in the operations that are published in `README.md`.  Specifically, it appears as though 'putting' a key and a value to the current python client object will actually create a `kinetic.common.Entry` object instead of `kinetic.client.Versioned`.  Additionally, a `kinetic.common.Entry` object does not appear to have a `data` attribute, but rather a `value` attribute.  See the following:

```
>>> from kinetic import Client
>>> c = Client('localhost', 8123)
>>> c.put('mykey', 'myvalue')
True
>>> c.get('mykey')
<kinetic.common.Entry object at 0x273ed50>
>>> c.get('mykey').data
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Entry' object has no attribute 'data'
>>> c.get('mykey').value
'myvalue'
```

This changeset introduces a change in the public-facing `README.md` doc such that it correctly reflects the state of the python client.