Building ipywidgets documentation

To build the ipywidgets documentation:

1. Install the development version of ipywidgets with the dev-install.sh script in the repo root directory.

2. Install the Python packages for building documentation with either mamba or conda:

   conda env update --file docs/environment.yml

   or with pip:

   python -m pip install -r docs/requirements.txt
   # Also install pandoc separately

3. Build the HTML docs with sphinx:

   cd docs/source
   python -m sphinx -T -E -b html -d ../build/doctrees -D language=en . ../build/html

4. Open the documentation from the build directory: docs/build/html