Update documentation for 0.7 release

issues: fixes #1473 

In general this PR should be used to update documentation for upcoming 0.7 release
I mean you said: "As you can see, in the first three cases, we inferred the ``x`` and ``y``
labels from the pandas object", the first one and the third one are pandas objects, but actually the second case is not a pandas object. Is that clear enough, maybe I am not expressing well myself?