Display method for in-text accidentals about musicians-compendium

[mccarthy-m-g]

This commit solves this issue. For anyone curious: I chose to use different renderers for HTML and PDF outputs, and will be using inline R code to reference symbols. For example: `r f` will display a flat symbol using unicode in the HTML version and the musicography package in the LaTeX version.

The only downside to this approach is that:

1. I have to create a new R object whenever I want to include a new symbol.
2. I have to source() the _musicSymbols.R file containing the music symbol R objects at the start of any chapter I wish to use them in. This appears to be a limitation of the knitr::is_html_output() and knitr::is_latex_output() functions, as their documentation says they only work in .Rmd files. Calling _musicSymbols.R in _bookdown.yml with before_chapter_script: does not work.
3. The Bravura Text font doesn't seem to work in the epub version of this book.
4. The current implantation leaves symbols invisible while the font loads (I can change the css to uncomment font-display: swap; to change this behaviour though).