Fix for several musicxml2ly bugs. (issue 5697059)

[ptrcklschmdt]

Reviewers: ,

Description:
Fix for several musicxml2ly bugs.



musicxml2ly: title, chord symbol and midi bug

Titles and headers can now contain single words followed by a
 punctuation mark (.,!:).  See issue 1983.

Chord symbols are now placed above staffs instead of below.

musicxml2ly now includes an out-commented midi-block in every .ly-file.

Docs: Added command line options -m and --midi to Usage

Please review this at http://codereview.appspot.com/5697059/

Affected files:
  M Documentation/usage/external.itely
  M python/musicexp.py
  M python/musicxml.py
  M scripts/musicxml2ly.py