ABC assist

- guitar chords

Author: jwdj

CHANGES

@@ -566,4 +566,5 @@ different panes. Tie/untie option added for notes. Broken rhythm
   Search advanced using ABC-fields. For example: search all tunes with Mozart as composer and meter 3/4:
     C:mozart M:3/4
 - Added exclusive mode: only one file is allowed
-    Exlusive mode is enabled via command line option -exclusive
+    Exlusive mode is enabled via command line option -exclusive
+- ABC assist: Support for %%MIDI gchord