Release 0.4.0

[bollwyvl]

• merge all outstanding PRs
  • Refresh environments #49
  • Add suffix to menu items locator #46 & Update locator to use p-mod-hidden class #52
  • Update docs for 0.4.0 release #51
  • ???
• start a release issue with a checklist (maybe like this one)
• ensure VERSION has been increased appropriately
• ensure the HISTORY.ipynb is up-to-date
• validate on binder
• validate on ReadTheDocs
• wait for a successful build of master
• download the dist archive and unpack somewhere (maybe a fresh dist)
• create a new release through the GitHub UI
  • paste in the relevant HISTORY entries
  • upload the artifacts
• actually upload to pypi.org

  doit publish

• postmortem
  • handle conda-forge feedstock tasks
  • validate on binder via simplest-possible gists
  • activate the version on ReadTheDocs
  • bump to next development version
  • update release procedures