Diamond-shaped noteheads are not generated.

[joaocc]

See moinejf/abc2svg#31 for a more complete description of the symbol, as well as the desired ABC format output.

As of v66, xml2abc doesn't generate these from MusicXML generated from Dolet 6.6 on Sib 8.8

			<direction>
				<direction-type>
					<?DoletSibelius Unknown symbol index 331?>
					<other-direction default-y='10' relative-x='-1'>Diamond whole note</other-direction>
				</direction-type>
			</direction>

or

			<direction>
				<direction-type>
					<?DoletSibelius Unknown symbol index 331?>
					<other-direction default-y='14'>Diamond whole note</other-direction>
				</direction-type>
			</direction>