Gibbs state

[aidanstrathearn]

Pull Request Check List

This checklist serves as a guide for contributors and maintainers to assess
whether a contribution can be merged into the main branch and thus serves
to guarantee the quality of the package. Please also read the
contribution guideline.

Before you submit a pull request, please go through this checklist once
more, as it will decrease the number of unnecessary review cycles.
However, this list is there to help all contributors to produce high
quality code, not to deter you from contributing. If you can't tick some of the
boxes, feel free to submit the pull request anyway and report about it in the
pull request message. Also, some of the boxes might not apply to the specific
type of your contribution.

• The contribution has been discussed and agreed on in the Issue section.
• Code contributions do its best to follow the zen of python.
• The automated test are all positive:
  • tox -e py36 (to run pytest) the code tests.
  • tox -e style (to run pylint) the code style tests.
  • tox -e docs (to run sphinx) generate the documentation.
• Added test for changed/added code.
• API code contributions include input checks (defensive code).
• API code contributions include helpful error messages.
• The documentation has been updated:
  • docstring for all new functions/methods/classes/modules.
  • consistent style of all docstrings.
  • for new modules: /docs/pages/modules.rst has been updated.
  • for api contributions: /docs/pages/api.rst has been updated.
  • for api contributions: tutorials and examples have been updated.

[gefux]

Thank you @aidanstrathearn for this major contribution!