Add trill spanner with accidental

[dbenjaminmiller]

I'm currently using a hack to achieve this; a slightly more general version would accept any character as an argument (currently doing manual positioning, but I'm certain a better way is obvious).

#(define (ekm-trillspansharp grob)
  (let* ((ext (ly:stencil-extent (ly:grob-property grob 'stencil) X))
         (tr (ekm-ctext grob 0 (markup #:ekm-combine #xE566 2.3 0.5 #xE262 #:hspace 0.25) ))
         (tr (ly:stencil-translate-axis tr (car ext) X))
         (tempo (ly:grob-property grob 'text))
         (seg (- #xEAA4 (if (integer? tempo) (min 4 (max -4 tempo)) 0))))
    (ly:grob-set-property! grob 'stencil
      (ly:stencil-combine-at-edge
        tr
        X RIGHT
        (grob-interpret-markup grob
          (make-ekm-chars-markup (make-list
            (inexact->exact (floor
              (/ (- (interval-length ext) (ekm-extent tr X))
                 (ekm-extent (ekm-cchar grob 0 seg) X))))
            seg)))
        0))))