Implemented material versionining.

All versioning commands now work with material packages.

These are (vdmo), (vlyo), (vpdfo), (vomo) and (vdls).

Example:

    Red Example Score (2013) - materials - tempo inventory

        definition module - edit (dme)                     repository - add (rad)
        definition module - interpret (dmi)                repository - commit (rci)
        definition module - write stub (dmws)              repository - revert (rrv)
                                                           repository - status (rst)
        go - back (b)                                      repository - update (rup)
        go - home (h)
        go - score (s)                                     system - LilyPond log (ll)
                                                           system - Python (pyi)
        go - next score (>>)                               system - commands (?)
        go - next asset (>)                                system - doctest (pyd)
        go - previous score (<<)                           system - pytest (pyt)
        go - previous asset (<)                            system - quit (q)
                                                           system - session variables (sv)
        go - build (u)                                     system - shell (!)
        go - distribution (d)
        go - makers (k)                                    versions - definition.py - open (vdmo)
        go - materials (m)                                 versions - illustration.ly - open (vlyo)
        go - segments (g)                                  versions - illustration.pdf - open (vpdfo)
        go - stylesheets (y)                               versions - output.py - open (vomo)
                                                           versions directory - list (vdls)
        go - edit current stylesheet (Y)

        illustrate module - write stub (imws)

        illustration ly - interpret (lyi)
        illustration ly - open (lyo)

        illustration pdf - open (pdfo)

        material - autoedit (mae)
        material - illustrate (mi)

        metadata - add (mda)
        metadata - get (mdg)
        metadata - remove (mdrm)
        metadata module - open (mdmo)
        metadata module - rewrite (mdmrw)

        output module - open (omo)
        output module - write (omw)

        package - initializer - open (ino)
        package - initializer - write stub (inws)
        package - unadded assets - remove (uar)
        package - unset autoeditor (pua)
        package - version artifacts (ver)

    >