Bugfix/code clean using gcc warnings (#371)

* Enable extra GCC warnings to discover subtle bugs

* convert c++ comments to c comments

* cleanup pedantic compiler warnings

* Compile apps with GNU89 GNU99 GNU11 and GNU17

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

apps/initrouter/main.c

@@ -241,9 +241,9 @@ static void print_help(char *filename)
 {
     printf(
         "Send BACnet Initialize-Routing-Table message to a network\n"
-        "and wait for responses.  Displays their network information.\n"
-        "\n"
-        "address:\n"
+        "and wait for responses.  Displays their network information.\n");
+    printf("\n");
+    printf("address:\n"
         "MAC address in xx:xx:xx:xx:xx:xx format or IP x.x.x.x:port\n"
         "DNET ID Len Info:\n"
         "Port-info data:\n"