I used a variant on the pattern described here to run "npm run build" when
creating the wheel:
http://cra.mr/2014/12/19/distributing-js-with-python
To generate just the static assets (in datasette_vega/static) run this:
python3 setup.py build_static
To build the package (and automatically run the above) do this:
python3 setup.py bdist_wheel
