This PR addresses feedback from the mailing list and a recent pull request to BIP 3. The following functional changes are made:
- Revert the recently added AI guidance
- Broaden the formats per which reference implementations may be provided
- Move Type header responsibility to the author(s)
A Changelog section is added and backfilled, and a few editorial improvements are made. The Version header is omitted at this time, since it is not permitted under BIP 2.