lengthcheck: ignore comments
lengthcheck: option to print full source of each defect score
lengthcheck: accept note with forced accidental
lengthcheck: count lyric skips correctly
lengthcheck: option to skip scores with empty music/lyrics
lengthcheck: rename option score -> source
lengthcheck: option to output reports as lilypond markup

together with --source allows easy visual control of detected defects
LilyPondMusic copes with a file without scores