document InvalidURL exception

Doc/lib/libhttplib.tex

@@ -57,6 +57,11 @@ subclass of \exception{Exception}.
 A subclass of \exception{HTTPException}.
 \end{excdesc}
 
+\begin{excdesc}{InvalidURL}
+A subclass of \exception{HTTPException}, raised if a port is given and is
+either non-numeric or empty.
+\end{excdesc}
+
 \begin{excdesc}{UnknownProtocol}
 A subclass of \exception{HTTPException}.
 \end{excdesc}