Release 3.9.0 (plotly#1552)

* CHANGLELOG for 3.9.0
* README with release candidate versions in install instructions

Update widget to 0.10.0-rc.1

Release 3.9.0 (plotly#1552)

* CHANGLELOG for 3.9.0
* README with release candidate versions in install instructions

Update widget to 0.10.0-rc.1

Release 3.8.1 (plotly#1530)

* Update CHANGELOG and README for 3.8.1
* Update plotlywidget version to 0.9.1

Release 3.8.1 (plotly#1530)

* Update CHANGELOG and README for 3.8.1
* Update plotlywidget version to 0.9.1

Release 3.8.0 (plotly#1518)

* CHANGELOG and README updates
* Bump plotlywidget version
* align hoverlabels left and constant-size legend items in builtin themes (plotly#1520)
* update generated templates
* update widget version to 0.9.0

Release 3.8.0 (plotly#1518)

* CHANGELOG and README updates
* Bump plotlywidget version
* align hoverlabels left and constant-size legend items in builtin themes (plotly#1520)
* update generated templates
* update widget version to 0.9.0

package build

package build