DOC: Fix Doxygen special command markup and provide example

Fix Doxygen special command markup: use a single backslash.

Provide an example of the use of such commands.

Author: jhlegarreta

SoftwareGuide/Latex/Appendices/CodingStyleGuide.tex

@@ -274,8 +274,9 @@ \subsection{Doxygen Documentation System}
 Doxygen requires the embedding of simple comments in the code which is in turn
 extracted and formatted into documentation.
 
-Note that ITK prefers the backslash (\code{\textbackslash\textbackslash})
-style versus the at-sign (\code{@}) style to write the documentation commands.
+Note that ITK prefers the backslash (\code{\textbackslash}) style versus the
+at-sign (\code{@}) style to write the documentation commands (e.g.
+\code{\textbackslash{}class}).
 
 For more information about Doxygen, please visit
 \href{http://www.stack.nl/~dimitri/doxygen/}{http://www.stack.nl/~dimitri/doxygen/}