Customization commands

[jperon]

This PR includes several tools for customization:

• \lynewenvironment lets one define wrappers for ly without most of the drawbacks mentionned in the doc (especially the [] for empty optional arguments);
• as \lynewenvironment doesn't allow adding lilypond code between \begin{ly} and \end{ly} (but only latex code before and after), four new parameters allow it in various places, which must be defined to a filename (or a list of filenames) to include (without '.ly'):
  • include_header;
  • include_footer;
  • include_before_body;
  • include_after_body;
• \lysavefrag{FILE} allows defining lilypond code to be saved to tmp-ly/FILE.ly, so that it may be called from include_....

[jperon]

Here is a MWE:

\documentclass{scrartcl}
\usepackage[debug]{lyluatex}

\begin{document}

\lynewenvironment{myly}[1][]{%
    {\centering test \par}
    \begin{ly}[
        include_before_body={foot,foot},
        include_after_body=head,
    ]
}{
    \end{ly}
}

\begin{lysavefrag}{head}
a b c
\end{lysavefrag}

\begin{lysavefrag}{foot}
g a' b
\end{lysavefrag}

\begin{myly}
d e f
\end{myly}

\end{document}

[uliska]

This looks very interesting. I'll look into it, but most probably not today.

[uliska]

I admit I don't really understand the code changes, so I can only state that both the MWE and the manual work with the modified content.

I have applied a few clarifications to the manual because I think people will be confused by a caption argument with the actual content "caption", or with "saved fragments" that are all named like they are keywords.

So from my perspective this can can be merged.