[GLISS] differentiating pre/post/neutral commands

[Graham Percival]

Continuing to brainstorm on the problem of it not being obvious to
which note a particular \command refers to, what if we used:

\postfix:      c2 d\p  is unchanged
/prefix: for music functions like   c2 /parenthesize d
.neutral: for commands which aren't attached to notes, such
  as .clef or .times.

   .version "2.16.0"
   .score {
     /new Staff {
       .clef "bass"
       .times 3/4
       c4 /parenthesize d\p g .bar "|."
     }
   }


It's obviously not a fully-thought-through idea, but the whole
point of brainstorming is to list not-fully-thought-through ideas.

- Graham