This commit resolves all outstanding duplicate label
and duplicate citation warnings.
I have not yet addressed unreferenced footnote warnings.
I took the general strategy of replacing a target above a section heading
with references directly to that section heading,
or where impractical, disambiguting the target with ``PEP NNN``.
I also converted all the citations in PEP 482 to links,
as they were causing duplicate citation warnings.
* Lint: Clarify name/ID of required header check
* PEP 440: Fix header ordering
* PEP 441: Fix header ordering
* PEP 523: Fix header ordering
* PEP 612: Fix spurious top-level title section heading
* Lint: Add new check for consistant PEP header order
Changes detected by Topy (https://github.com/intgr/topy), all changes
verified by hand, false positives have been omitted.
These range from straight-out misspellings to debatable hyphen placement.
The hyphen changes are supported by grammar manuals of style.
* making indentation consistent
* small alteration to section structure
* providing a bit more context for the 'User Defined Generic Classes' section
* missing 'and'