9.0.0

Change

• e9f34ee Change to require Node.js 16
  migrate: update too
• ffb64b2 Change to use exports
  migrate: don’t use private APIs
• 89fbc0b Update mdast-util-toc, @types/mdast, etc
  migrate: update too
• 6fbf704 Change to include Contents headings by default
  migrate: pass an options.heading if you don’t want it
• 64f5cd9 Change to default to tight: true
  migrate: pass options.tight: true if you don’t want it

Full Changelog: 8.0.1...9.0.0