This pull request introduces a new utility function to the k1LoW/errors package for splitting joined errors, updates the documentation to reflect this addition, and adds comprehensive tests to ensure correct behavior.

New functionality

• Added a new Errors function to errors.go that recursively splits joined errors and returns all underlying errors as a flat slice.

Documentation updates

• Updated the "Key features" list in README.md to mention the ability to split joined errors.
• Updated the comparison section in README.md to include the new Errors function alongside existing features.

Testing

• Added a new TestErrors unit test in errors_test.go to verify the correct splitting of joined and nested joined errors, as well as handling of non-joined errors.