Added :ds: and :path: tokens to view microlanguage.

Example:

    Red Example Score (2013) - materials

       1: instrumentation (AE)
       2: magic numbers
       3: pitch range inventory (AE)
       4: tempo inventory (AE)
       5: time signatures

          materials - copy (cp)
          materials - new (new)
          materials - remove (rm)
          materials - rename (ren)

    > vap

    Red Example Score (2013) - materials - select view to apply:

       1: autoeditable
       2: inventories
       3: magic

    > inventories

    Red Example Score (2013) - materials (inventories)

       1: pitch range inventory (AE)
       2: tempo inventory (AE)

          materials - copy (cp)
          materials - new (new)
          materials - remove (rm)
          materials - rename (ren)

    > vcl

The 'inventories' view is defined equal to "'inventory' in :ds:" which means
that the string 'inventory' appears in the asset display string.

The other new token is :path: which can be used in the same way for asset path.