* scripts/musicxml2ly.py (print_voice_definitions): new function

* scripts/musicxml2ly.py (print_voice_definitions): new function
(print_score_setup): new function
(convert): read part definition to output staves properly.

* python/musicxml.py (Measure.get_notes): new class. Wrap lists of
Music_xml notes.

* python/musicexp.py (Output_printer.__init__): use _ in data members.
(Output_printer.unformatted_output): new function: no formatting,
but count braces.
(Duration.get_length): remove isinstance() checks for Output_printer everywhere.

* input/regression/lyrics-bar.ly (texidoc): add Separating_line_group_engraver.