LilyPond diamond noteheads

Black and white diamond noteheads are easy now.

   \new Staff {
      \set Score.proportionalNotationDuration = #(ly:make-moment 1 16)
      \override Staff.TimeSignature #'transparent = ##t
      \once \override NoteHead #'style = #'harmonic-black
      d'4
      \once \override NoteHead #'style = #'harmonic
      d'4
   }

Thanks to Max. Previously 'harmonic-black and 'harmonic weren't available as NoteHead #'style options.