simplepost.c: fixed compiling with VS before 2015

doc/examples/simplepost.c

@@ -13,6 +13,11 @@
 #include <string.h>
 #include <stdlib.h>
 
+#if defined(_MSC_VER) && _MSC_VER+0 <= 1800
+/* Substitution is OK while return value is not used */
+#define snprintf _snprintf
+#endif
+
 #define PORT            8888
 #define POSTBUFFERSIZE  512
 #define MAXNAMESIZE     20