explicit void params declarations, add warnings to keep it correct

thx http://nickdesaulniers.github.io/blog/2019/05/12/f-vs-f-void-in-c-vs-c-plus-plus/

yaml.c

@@ -49,12 +49,12 @@ static const char keys_field_time[]      = "time: ";
 
 static pthread_mutex_t tminfo_mutex;
 
-void yamlout_init()
+void yamlout_init(void)
 {
 	pthread_mutex_init(&tminfo_mutex,0);
 }
 
-void yamlout_clean()
+void yamlout_clean(void)
 {
 	pthread_mutex_destroy(&tminfo_mutex);
 }