[LSR-620] Vertical line as a baroque articulation mark

[Pierre Perol-Schneider]

Hi Squad Members,

Regarding this snippet:
http://lsr.di.unimi.it/LSR/Item?id=620
I'm not sure about the 'font-size 3' effect; was it for the articulation
line thickness?
Anyway I'm thinking about putting a more user-friendly script.
How about:

upline =
#(define-event-function (parser location) ()
   #{
      %% possible tweaks here, e.g:
      %-\tweak padding #1
      %-\tweak avoid-slur #'around
      %-\tweak direction #DOWN
      -\tweak stencil #(lambda (grob) (grob-interpret-markup grob
                          #{
                             \markup
                             \override #'(thickness . 3)
                             \draw-line #'(0 . 1)
                          #}))
       \stopped
   #})

\relative c' {
  a'4^\upline a( c d')_\upline
}

Cheers,
Pierre