logger changes from global static variables to one instance per stellar

src/log/log_private.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+#include "stellar/log.h"
+
+extern thread_local struct logger *__thread_local_logger;
+
+struct logger *log_new(const char *config_file);
+void log_free(struct logger *logger);
+void log_level_reload(struct logger *logger);
+
+#ifdef __cplusplus
+}
+#endif