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- Remove sphinx.util.force_decode. Previously we hacked it in to support Python
2 and Sphinx 3.x, but Sphinx 4.0 deprecated it and dropped Python 2 support.
- Replace Travis-CI with GitHub Actions
- Add support for Python 3.6, 3.7, 3.8, 3.9, 3.10, and PyPy3.
- Drop support for Python 2.7, 3.3, 3.4, 3.5, and PyPy.
- Update to work with newer Sphinx versions:
* Sphinx.domains -> Sphinx.registry.domains
* Sphinx.override_domain(D) -> Sphinx.add_domain(D, override=True)
- Drop support for Sphinx < 4.0.