Improved (lyi) user experience.

The command now messages what it will change before doing so AND also messages
what it is changing as it is doing so.

Example:

   Red Example Score (2013) - segments

      1: segment 01
      2: segment 02
      3: segment 03

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

   > lyi

   Will interpret ...

    INPUT: /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_01/output.ly
   OUTPUT: /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_01/output.pdf

    INPUT: /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_02/output.ly
   OUTPUT: /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_02/output.pdf

    INPUT: /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_03/output.ly
   OUTPUT: /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_03/output.pdf

   Ok? y

   Interpreted '/Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_01/output.ly'.
   Wrote '/Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_01/output.pdf'.

   Interpreted '/Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_02/output.ly'.
   Wrote '/Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_02/output.pdf'.

   Interpreted '/Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_03/output.ly'.
   Wrote '/Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_03/output.pdf'.

   >