Add SourceDirectory - with current restrictions.

Closes modelica#2145

chapters/functions.tex

@@ -2101,6 +2101,11 @@ \subsection{Annotations for External Libraries and Include Files}\label{annotati
   \item
     \lstinline!"linux64"! (Linux Intel 64 bit)
   \end{itemize}
+\item
+  The
+  \lstinline!annotation(SourceDirectory="modelica://ModelicaLibraryName/Resources/Source")!\annotationindex{SourceDirectory}, gives the location for source files.
+  The preceding one is the default and need not be specified; but another location could be specified by using an URI name for the source directory, see \cref{external-resources}.
+  It is not specified how they are built.
 \end{itemize}
 
 The \filename{win32} or \filename{win64} directories may contain \filename{gcc47}, \filename{vs2010}, \filename{vs2012}
@@ -2120,7 +2125,7 @@ \subsection{Annotations for External Libraries and Include Files}\label{annotati
 compatible with vs2005.
 \end{nonnormative}
 
-The \lstinline!ModelicaLibraryName! used for \lstinline!IncludeDirectory! and \lstinline!LibraryDirectory! indicates the top-level class where the annotation is found in the Modelica source code.
+The \lstinline!ModelicaLibraryName! used for \lstinline!IncludeDirectory!, \lstinline!LibraryDirectory!, and \lstinline!SourceDirectory! indicates the top-level class where the annotation is found in the Modelica source code.
 
 \begin{example}
 Use of external functions and of object libraries: