Support for Leaf Bundle

[rokuosan]

Feature overview

The Leaf Bundle function provided by Hugo has the following directory structure diagram, and I would like to be able to output according to this diagram.

content/
├── about
│   ├── index.md
├── posts
│   ├── my-post
│   │   ├── content1.md
│   │   ├── content2.md
│   │   ├── image1.jpg
│   │   ├── image2.png
│   │   └── index.md
│   └── my-other-post
│       └── index.md
│
└── another-section
    ├── ..
    └── not-a-leaf-bundle
        ├── ..
        └── another-leaf-bundle
            └── index.md

Reason

Because we want to make it available to themes like Stack.