[docs] [issue30096] Update examples in abc documentation to use abc.ABC

[Eric Appelt]

Eric Appelt added the comment:

I created a PR to update the documentation to use this pattern and follow Raymond's suggestion of showing both ways to define an abc.

In order to make the examples comprehensible when read from beginning to end, I reordered the classes so that abc.ABC is described first.

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nosy: +Eric Appelt

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30096>
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