replace C-style include files with their C++ equivalents

src/pair_coul_wolf.cpp

@@ -15,10 +15,10 @@
    Contributing author: Yongfeng Zhang (INL), yongfeng.zhang@inl.gov
 ------------------------------------------------------------------------- */
 
-#include <math.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <cmath>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
 #include "pair_coul_wolf.h"
 #include "atom.h"
 #include "comm.h"