Release 4.0.0

[kasparsd]

Release Changelog

• Fix: Describe a bug fix included in this release.
• New: Describe a new feature in this release.

Release Checklist

• [x] This pull request is to the master branch.
• [x] Release version follows semantic versioning. Does it include breaking changes?
• [x] Update changelog in readme.txt.
• [x] Bump version in stream.php.
• [x] Bump Stable tag in readme.txt.
• [x] Bump version in classes/class-plugin.php.
• [x] Draft a release on GitHub.

Change [ ] to [x] to mark the items as done.