Update default Texinfo documentation models.
    
     - Don't store chapter files definitions inside the Chapter directory.
       Instead, use the Chapter directory name as reference to create
       files at the same level it is. See the following directory tree,
       example:
    
       en_US/
       |-- Chapters
       |   |-- section-functions.texinfo
       |   `-- section.texinfo
       |-- Chapters-menu.texinfo
       |-- Chapters-nodes.texinfo
       `-- Chapters.texinfo