PEP 7: Remove Python 2.2 advice, add C syntax highlighting and green/red sidebars

[hugovk]

• Remove the section "For C code that needs to support versions of Python older than 2.3...". I can add it back if needed.

• Highlight the example C code with C syntax instead of Python.

• Like PEP 8 (PEP 8: Add green and red sidbar for good and bad examples #3567), add green and red side borders "good" and "bad" examples. For this, I split this example into two blocks:

      return albatross; /* correct */
      return(albatross); /* incorrect */

• Format None as None, add a missing full stop. Remove some redundant PEP fields.

Example

Before	After

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📚 Documentation preview 📚: https://pep-previews--3702.org.readthedocs.build/pep-0007/

[willingc]

Lovely @hugovk