Prepare release 1.26.0

[cicirello]

Summary

Prepare release 1.26.0, including updating documentation.

Pull Request Requirements

If you are unable to check everything in this list, your pull request will be closed:

• I have read the CONTRIBUTING document.
• My pull request has a corresponding Issue and I linked to it above in the Closing Issues section.

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvements to existing code, such as refactoring or optimizations (non-breaking)
• Breaking change (fix or feature that would cause existing functionality to change)
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.