pep8ify examples/ part 3

``examples/pylab_examples``, ``examples/units`` and ``examples/use_interface`` remain to be done.
It doesn't say that explicitly, but it is entirely consistent with what it does say.  Look at the section that @ianthomas23 quoted above.  Note the "..consider adding...".  Granted, the first "yes" example is ```i = i + 1```; but there is *nothing* in the "no" examples, or the text, to indicate that ```i = i+1``` would be considered *unacceptable*.  Note the words "Use your own judgment...".