Aliased __str__ to __repr__

[jlstevens]

PR implementing the suggestion in #966. The code change is tiny (aliasing __str__ to __repr__) and most of this PR will be about updating the docs.

Here is the behavior before:

And after:

Of course I'll make sure to put the parens around print in the notebooks for Python 3 support!

[jlstevens]

I've now updated all the notebooks using print(repr(..)) and I have been careful to make sure the notebook tests kept passing.

Unfortunately, there are two notebooks with fixes that I do expect will result in test failures. These involve use of naked repr(..) which should result in different output (due to extra quotes compared to print).

[jlstevens]

As expected the tests failed. I thought only one cell would fail, but as repr returns a string whereas print outputs to standard output, the test data is now shifted. Rebuilding the test data now.

[jlstevens]

Now the test data has been updated, the pr build passed and the push build failed (as expected). Ready to review/merge.

[philippjfr]

Looks good. Happy to merge.