Shorten heading, making it more general

The previous heading didn't cover the new SourceDirectory annotation, so the headed needed some kind of adjustment anyway.

chapters/functions.tex

@@ -2361,7 +2361,7 @@ \subsection{Aliasing}\label{aliasing}
 The use of the function \lstinline!foo! in Modelica is uninfluenced by these considerations.
 \end{example}
 
-\subsection{Annotations for External Libraries and Include Files}\label{annotations-for-external-libraries-and-include-files}
+\subsection{Annotations for External Functions}\label{annotations-for-external-libraries-and-include-files}
 
 The following annotations are useful in the context of calling external functions from Modelica, and they should occur on the \lstinline!external!-clause and no other standard annotations should occur on the \lstinline!external!-clause.
 They can all specify either a scalar value or an array of values as indicated below for the \lstinline!Library! annotation: