Allow using ASCII for sharp signs

[jeandeaual]

Thanks for writing this awesome library!

I noticed that the tablature format used by default (tsugaru-signs) uses the ♯ (MUSIC SHARP SIGN) character for sharps, which makes sense, but doesn't align well with other numbers in a chord:

This PR adds tsugaru-signs-ascii as an option, which uses # instead, for a more consistent look:

The second commit makes \tsugaruNotation take the tablature as an argument (unfortunately mandatory since music functions need at least one mandatory argument to have optional arguments), but if that's unnecessary I can remove it.

Here is the code used for testing:

\version "2.20.0"

\include "shamisen.ly"

#(set-global-staff-size 32)

\header {
  tagline = ##f
}

\paper{
  page-breaking = #ly:one-line-auto-height-breaking
  #(define fonts
    (set-global-fonts
     #:roman "IPAexGothic"
     #:factor (/ staff-height pt 20)
    ))
}

\score {
  \new TabStaff \with { stringTunings = #niagariTuning } {
    \shamisenNotation #tsugaru-signs-ascii
    \time 2/4

    <c b c'>2 |

    \bar "|."
  }
}

[jeandeaual]

I realized the PDF I created didn't use IPAexGothic for the tab notation for some reason. With IPAexGothic, the output looks way better with the default tablature format, so this PR might not be very useful…