Document treq's default behavior to buffer responses

[gruns]

treq's documentation is devoid of explanation of the unbuffered parameter.

• https://www.google.com/search?q=site%3Atreq.readthedocs.org+%22buffer%22&oq=site%3Atreq.readthedocs.org+%22unbuffered%22

No comments, either.

$ grep -riI "unbuffered" treq/
./client.py:        if not kwargs.get('unbuffered', False):
./test/test_client.py:        d = self.client.get('http://www.example.com', unbuffered=True)

The behavior to buffer responses by default differs from t.w.c.Agent, which doesn't. This behavior is unexpected. It should be documented.

Where should it be documented? I'll submit a pull request.

[twm]

The unbuffered parameter is now documented and used in an example as of #233, so I'm closing this as complete. Thanks!