mention C17

Author: vladak

intro.tex

@@ -460,7 +460,8 @@
 C99+TC1+TC2+TC3, WG14~N1256, dated 2007-09-07.  It is a work in progress,
 with its current final draft located here,
 \url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf}.
-\item After C99, C11 came, officially ISO/IEC 9899:2011.
+\item After C99, C11 came, officially ISO/IEC 9899:2011. And then C17 in 2018,
+officially ISO/IEC 9899:2018.
 \item Some difference between C89 and C99 -- inline functions, variable
 definitions intermixed with code, one-line comments using \texttt{//}, new
 functions like \funnm{snprintf}() etc.