Update Python 2 syntax and drop Python-2-only examples.
Fix all Python console prompts to the full ">>> " for correct
highlighting.
Use "pycon" instead of "python" for interactive Python console session.
The "python" lexer is for Python scripts and doesn't interpret the ">>>"
prompt.
Fix all Python console code blocks to more accurately display what the
user will see. For example, when assigning a value to a variable, it
isn't also echoed.
Fix typo ".. code::" → ".. code-block::".
Use "console" instead of "sh" for shell sessions. The "sh" lexer is for
shell scripts. For a complete list of lexers, see:
https://pygments.org/docs/lexers/
Use blacken-docs to run black on code blocks. This is now included as a
pre-commit hook.