v0.26.1

• Fix bug that accidentally caused dartdoc to create (and overwrite with)
  multiple snapshots in parallel for a single tool (#1861, #1862)
• Refactor comment reference handling for performance and readability (#1863)
• Simplify temp file creation and reduce the amount of filesystem churn
  for tools (#1865)
• Reenable testing for flutter plugin doc generation (This requires
  a Flutter SDK with flutter/flutter#25243 to work with tools enabled).
  Flutter plugin doc generation now requires your flutter installation to have
  'flutter update-packages' run on it before it will work.