Add modal transformations provided by Mike Ellis (issue4079064)

[tdanielsmusic]

Reviewers: ,

Message:
This is a continuation of Issue 4126042.  I had to start a new Rietfeld
number as I'd moved to a new branch after rebasing and resolving merge
conflicts in preparation for pushing ... then Neil's comments arrived.
Sorry Neil - I think I've responded to all your comments correctly, but
the direct comparison with the previous upload is unavailable, so it
won't be so easy for you to check.

Trevor

Description:
Add modal transformations provided by Mike Ellis

- this is a continuation of 4126042 after rebasing

- and after responding to Neil's comments

Please review this at http://codereview.appspot.com/4079064/

Affected files:
  M Documentation/notation/pitches.itely
  A input/regression/modal-transforms.ly
  M ly/music-functions-init.ly
  M scm/lily.scm
  A scm/modal-transforms.scm