Release 3.2.0 (plotly#1157)

* Initial changelog work

* More progress on Changelog

* README installation updates to add conda and orca instructions

* Add notebook and ipywidgets to quickstart installation command

* Split quickstart code into two cells to show where figure is displayed

* Reorganize README

* Specialize schema descriptions for Python in docstrings

* bump versions to plotly.py 3.2.0rc1 and plotlywidget 0.3.0-rc.1

Also update README with release candidate installation instructions

* Conda needs single equals

* Fix conda orca install command
[skip ci]

* Fill in remaining TODOs and references in changelog and README
[skip ci]

* `np.ascontiguousarray` is preserving the `WRITEABLE` flag now.
Copy explicitly so we don't make input array read-only.

* Add instructions to unset NODE_OPTIONS environment variable

This causes an error when using orca from the commandline.

* Bump plotly.py to 3.2.0 and plotlywidget to 0.3.0

Release 3.1.1 (plotly#1096)

* Updated CHANGELOG and README
* Added release process to contributing.md

Merge pull request plotly#674 from plotly/update-changelog

Update changelog.

Merge pull request plotly#658 from plotly/2.0.0

2.0.0

Merge pull request plotly#656 from plotly/frames-support

Improve `frames` support in graph_objs.py.