Font for comments in Modelica code

[HansOlsson]

Based on modelica/ModelicaSpecification#3665 (this especially an issue for comments using words like "illegal" or "literal"; where the fixed-width writing using a variable-width font looks odd).

Either include:

% Comments in listings looks better and more distinct from the actual code if set in a variable-width sans-serif font.
% However, just changing font family doesn't work for pdf.
% Hence, we make a different choice of font depending on the target format.
\ifpdf
\let\sffamilyifhtml\relax
\else
\let\sffamilyifhtml\sffamily
\fi

and change to: commentstyle=\color{commentcolor}\sffamilyifhtml,

or just

commentstyle=\color{commentcolor}

as this template is for generating pdf-files.

I can provide PR for either.

[sjoelund]

I can see that it does indeed look odd. My personal preference would be to use minted though...