Add PEP content to output files

[daneah]

Each output file currently has just the tags, title, and connection to other mentioned PEPs. This is easy enough to do, but doesn't let people understand what each PEP is in context as they browse it in Obsidian.

Outcome

• Each PEP has the full PEP body in the output Markdown, transformed appropriately as noted below.

Notes

The reStructuredText can't just be shoved into the Markdown file, because the syntax will conflict. Some things should probably be transformed as well because they don't have an easy parallel. An example is the :pep: reference syntax—that could be converted to links (and possibly remove some of the need for the current Mentions section in the process)

Some of the metadata in the front matter might be able to be kept. Obsidian supports front matter in Markdown and treats it separately and specially from the document. Some is redundant with existing tags.