change bar number font, position, and size; document default fonts have been changed

Serif: Linux Libertine O
Sans-serif: Linux Biolinum O
Monospace: DejaVu Sans Mono
done voice C
Fix incorrect octave in voice B b.73
Done voice D

Voice D includes clef changes (as in my written-out manuscript)
Due to its different range it wasn't practical to input it without
changing the clef
Clef changes will be added to the previously-completed voices soon.
Done voice E (no clef changes done currently---not needed for basic legibility)