Add FF 02 copyright message option

GrooveOverlay: Permit a different groove for part of a bar (single
   beat breaks, etc).

    Syntax:  GrooveOverlay   2.5,3,yourgroove  4,4.5,mygroove

   Rough code outline (in parse) would be:

 ... if chordoverlay active:
      1. Change the start/end points already figured so that (using
         the above example) 2.5 to 3 and 4 to 4.5 are silent (z!)
      2. Remember what was in the table before we made the changes :)
      3. process the bar normally for all the tracks
      4. for each arg saved in overlay:
             - create a new chordtable with all silence expect for the overlay part
             - switch groove
             - process
      5. Return to original groove
 ... update bar pointers


Enhance the html groove docs to <play> a sample for a clicked groove.

It might be easy to add the ability to set different chords for different
   tracks. For example, one might want a C Major chord, but a C7 for
   the arpeggio(s). I'm thinking that we might do "Arpeggio Chord XX"
   and handle it much like a RIFF is done right now. Would there be
   any point/usage?

It might be useful to have a "if file exists" test. Useful for
   conditional includes and things like that. Deciding what path to
   use might be a problem (current path, groove library, include)???


The -b/-B options do NOT work if the section includes any BEATADJUST
   commands.

Add a midi channel volume tracker and setter. This would permit
   midi-(de)cresc from a known (by mma) value.

Library docs --- add the time signature to the header.

Add Nashville chord notation in addition to roman.