multiple voices in pianoStaff wip
Hold merge for Pianostaff no 2, some restructure needed
avoid backup when skip
Merge pull request #404 from PeterBjuhr/musicxml

MusicXML multiple voices in PianoStaff
additional clefs
reset after PianoStaff
Merge pull request #405 from PeterBjuhr/musicxml

MusicXML more fixes
reset voices
move token_hash to docinfo, as discussed in issue #406
on saving autocompile not needed
tempo directions
add Page.image

as discussed in issue #406, todo: use it from the cache, without keeping
a pointer to the document...
avoid python errors
deepcopy needed
doctype
better clef support
Merge pull request #407 from PeterBjuhr/musicxml

MusicXML more fixes
Scaling of skips
initial setup #376
first iteration and reset #376