Added 'materials - tour next (mtn)' and 'materials - tour previous (mtp)'.

Description: use (mtn) and (mtp) to advance forward and backward to material
packages.

Availability: (mtn) and (mtp) are available anytime during material
management.

Example:

    Score manager - example scores

        1: Blue Example Score (2013)
        2: Green Example Score (2013)
        3: Red Example Score (2013)

        scores - new (new)

    > red

    Red Example Score (2013)

        build (u)
        makers (k)
        materials (m)
        segments (g)
        setup (p)
        templates (t)
        stylesheets (y)

    > m

    Red Example Score (2013) - materials

        1: magic numbers
        2: pitch range inventory
        3: tempo inventory

        new material - by hand (nmh)
        new material - with manager (nmm)

    > mtn

    Red Example Score (2013) - materials - magic numbers

        illustration builder - edit (ibe)
        illustration builder - edit & execute (ibex)
        illustration builder - execute (ibx)
        illustration builder - remove (ibrm)
        illustration builder - stub (ibs)

        material definition - boilerplate (mdbp)
        material definition - edit [mde]
        material definition - execute (mdx)
        material definition - execute & edit (mdxe)
        material definition - remove (mdrm)
        material definition - stub (mds)

        output ly - make (lym)

        output material - boilerplate (ombp)
        output material - make (omm)
        output material - remove (omrm)
        output material - view (omv)

        output pdf - make (pdfm)

        stylesheet - edit (sse)
        stylesheet - select (sss)

    > mtn

    Red Example Score (2013) - materials - pitch range inventory

        PitchRange('[A0, C4)')
        PitchRange('[C4, C8]')

        illustration builder - edit (ibe)
        illustration builder - edit & execute (ibex)
        illustration builder - execute (ibx)
        illustration builder - remove (ibrm)
        illustration builder - stub (ibs)

        output ly - make (lym)

        output material - boilerplate (ombp)
        output material - interact (omi)
        output material - remove (omrm)
        output material - view (omv)

        output pdf - make (pdfm)

        stylesheet - edit (sse)
        stylesheet - select (sss)

    > mtn

    Red Example Score (2013) - materials - tempo inventory

        Tempo(Duration(1, 8), 72)
        Tempo(Duration(1, 8), 108)
        Tempo(Duration(1, 8), 90)
        Tempo(Duration(1, 8), 135)

        illustration builder - edit (ibe)
        illustration builder - edit & execute (ibex)
        illustration builder - execute (ibx)
        illustration builder - remove (ibrm)
        illustration builder - stub (ibs)

        output ly - make (lym)

        output material - boilerplate (ombp)
        output material - interact (omi)
        output material - remove (omrm)
        output material - view (omv)

        output pdf - make (pdfm)

        stylesheet - edit (sse)
        stylesheet - select (sss)

    > mtn

    Red Example Score (2013) - materials - magic numbers

        illustration builder - edit (ibe)
        illustration builder - edit & execute (ibex)
        illustration builder - execute (ibx)
        illustration builder - remove (ibrm)
        illustration builder - stub (ibs)

        material definition - boilerplate (mdbp)
        material definition - edit [mde]
        material definition - execute (mdx)
        material definition - execute & edit (mdxe)
        material definition - remove (mdrm)
        material definition - stub (mds)

        output ly - make (lym)

        output material - boilerplate (ombp)
        output material - make (omm)
        output material - remove (omrm)
        output material - view (omv)

        output pdf - make (pdfm)

        stylesheet - edit (sse)
        stylesheet - select (sss)

    > q

Notice that the command cycles around from the last material to the first.