Improve markdown parsing

[isoos]

• Refactor markdown parsing (discussion)
• Remove package name from the beginning of the README.md (Remove title from README.md if it matches the package name #3238)
• Remove "Changelog" text from the beginning of the CHANGELOG.md (discussion)
• Document supported changelog formats
• Improve structured changelog parser
  • Accept styled elements inside a changelog header (discussion)
  • Support more version formats (discussion)
  • Consider limiting changelog structures to h1 and h2 levels. (discussion)

[kevmoo]

Re Remove package name from the beginning of the README.md (#3238)

Instead/also – consider it a style lint (small point drop) to include the title in the readme. It's gratuitous in all contexts (source repo, pub site, etc)

[kevmoo]

Ditto for "changelog" at the top of the changelog – do a small point drop for this! Encourage standard format!