add a couple missing items

Doc/lib/libcsv.tex

@@ -170,6 +170,16 @@ attributes, which are used to define the parameters for a specific
 \class{reader} or \class{writer} instance.
 \end{classdesc*}
 
+\begin{classdesc}{excel}{}
+The \class{excel} class defines the usual properties of an Excel-generated
+CSV file.
+\end{classdesc}
+
+\begin{classdesc}{excel_tab}{}
+The \class{excel_tab} class defines the usual properties of an
+Excel-generated TAB-delimited file.
+\end{classdesc}
+
 \begin{classdesc}{Sniffer}{}
 The \class{Sniffer} class is used to deduce the format of a CSV file.
 \end{classdesc}