Layered Generator

[astrsh]

Pull Request

Brief description.

What Issues Does This Fix?

Implements a new generator based on 'layers' as outlined in #340

Licensing

• [x] I am the original author of this code, and I am willing to release it under GPLv3.
• [ ] I am not the original author of this code, but it is in public domain or released under GPLv3 or a compatible license.

Goal of the PR

See #340

Affects of the PR

Types of changes

• [ ] Bug Fix
• [ ] Build system
• [ ] Documentation
• [x] New Feature
• [ ] Performance
• [ ] Refactoring
• [ ] Repository
• [ ] Revert
• [ ] Style
• [ ] Tests
• [ ] Translation

Compatiblity

• [ ] Breaking change
• [x] Non-Breaking change.

Contribution Guidelines.

• [x] I have read the CONTRIBUTING.md document in the root of the git repository.
• [ ] My code follows the code style for this project.

Documentation

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

Testing

• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.