* Fix typo in DEVELOPER.md, submitted by billykern.
* Improve and cleanup the Windows and PyCharm build process.
* Update build system to use poetry.core, submitted by Spectre5.
* Fix the GitHub test suite by adding Python version into cache id.
* Update isort to use the new black profile, submitted by Spectre5.
* Move to newer versions of various build dependencies (black, Sphinx, etc.).
* Standardize on UNIX line endings in Git working copy and PyPI package.
* Make improvements to Read the Docs integration, including a PR merge gate.
* Clean up badges shown in documentation, so they are links to something sane.
* Make improvements to the MyPy and Pylint configuration.
* Move to a new two-step release process based on cedar-backup3.
* Create a changelog for the first time, along with new release process.