Prepare for dartdoc 0.39.0. (#2480)

* Prepare for 0.39.0

* trivial formatting change

Prepare for 0.38.0. (#2451)

Prepare for dartdoc 0.37.0 (#2435)

* Prepare for dartdoc 0.37.0

* Update changelog for #2434

Prepare for 0.36.2. (#2415)

Prepare for dartdoc 0.36.1 (#2405)

Prepare for version 0.36.0. (#2399)

Prepare for dartdoc 0.35.0 (#2372)

* pubspec

* Update changelog

* Update CHANGELOG.md