Remove command-line option inconsistencies

Optional arguments, as parsed by the getopt_long mechanism, are
inherently inconsistent with how you define required arguments.

To avoid confusion we decide to avoid this inconsistency by replacing
optional options with additional options with required argmuments.

src/configfile.c

@@ -144,6 +144,13 @@ static int data_handler(void *user, const char *section, const char *name,
             }
         }
         else if (!strcmp(name, "timestamp"))
+        {
+            if (!strcmp(value, "enable"))
+            {
+                option.timestamp = TIMESTAMP_24HOUR;
+            }
+        }
+        else if (!strcmp(name, "timestamp-format"))
         {
             option.timestamp = timestamp_option_parse(value);
         }