MusicXML: Fix small issues detected with Recordare sample MusicXML files

MusicXML: Fix small issues detected with Recordare sample MusicXML files

-) Open the .ly output files using utf-8 encoding so that special characters
   like Umlaute, ©, » «, etc. can also be written out. Otherwise, python
	 will simply exit the script.
-) Fix line break issues with sys.stderr.write (line break explicitly needed
   in contrast to print)
-) Fix extraction of creator from the XML. In particular, don't look only at
   the very first creator tag, but loop through all of them. Now, a score
	 can have a composer, a lyricist, etc.
-) Extract lyrics syllables only for notes, but not for rests. In lilypond
   a rest can have lyrics attached, in lilypond, the lyrics are assigned to
	 notes only. All lyrics assigned to rests in MusicXML will be lost!

Signed-off-by: Reinhold Kainhofer <reinhold@kainhofer.com>