Add /chordGlissando to music functions (issue3530042)

[Carl . D . Sorensen]

Reviewers: ,

Message:
In response to requests from the tablatures list, I've added this
function to ly/music-functions-init.ly.

I'm not totally sure that this should be part of the default lilypond
installation.  It seems a bit hacky to me.

Please review.

Thanks,

Carl


Description:
Add /chordGlissando to music functions

Please review this at http://codereview.appspot.com/3530042/

Affected files:
  A input/regression/tablature-chord-glissando.ly
  M ly/music-functions-init.ly