0.4.0

Breaking

• Drop support for Python < 3.7.

• Changelog releaser now uses the unreleased name "TBD" instead of "Master".
  CHANGELOG.md files must use "TBD" as the upcoming release name going
  forward.

Enhancements

• Support using branches named main as a default branch (previously default
  branches had to be named master).

• Repo commands now sort the list of repositories to provide a consistent
  experience across macOS and Linux platforms.