Added Menu.make_navigation_section() method.

Navigation menu sections are like this:

    Red Example Score (2013)

        build (u)
        distribution (d)
        makers (k)
        materials (m)
        segments (g)
        setup (p)
        stylesheets (y)

    > q

Navigation sections are not command sections.

Navigation sections are not detailed by (?).

The purpose of (?) is to detail commands.