Update repository user's guide:
    
        - Don't use the same directories layout used inside the repository
          as chapter or sections. Instead use the conceptual ideas that
          make that directory layout to exist.
    
        - In this commit I completly remove the Directories part of the
          guide in the sake of a better reorganization, as described in
          the paragraph above. A major problem I found whith using
          directories layout as chapters or sections is the horizontal
          legth required which in some cases exceeds the phisical page of
          PDF documents. Shorter names for chapters and sections seems to
          be preferable than long ones.