7.0.0

• cf30f38 Change API to allow different instances
  migrate: now, createEmphasize, all, and common are exported;
  do createEmphasize() to create an emphasize with nothing yet,
  createEmphasize(common) for one with common languages, etc;
  this also renames registerLanguage to register
• adad2aa Update lowlight
  migrate: make sure to register languages you want with emphasize itself
• 58bff2d Change to require Node.js 16
  migrate: update too
• f675f03 Change to use exports
  migrate: don’t use private APIs

Full Changelog: 6.0.0...7.0.0