logger: make logger thread-safe

The commit replaces non-thread-safe `localtime` function call with
thread-safe `localtime_r` - it uses external buffer instead of internal
static one under the hood to achieve thread-safety.

Note that logger uses `std::cout` and `std::cerr` - to my surprise, they
are actually thread-safe, but parts of the messages sent from different
threads can get mixed. That's not great, but anyway the log is mostly
used to report errors, and they are pretty rare. So, as long as it is
not UB, such implementation is acceptable.

Part of #110

Author: drewdzzz

src/Utils/Logger.hpp

@@ -73,7 +73,8 @@ class Logger {
 			return;
 		time_t rawTime;
 		time(&rawTime);
-		struct tm *timeInfo = localtime(&rawTime);
+		struct tm buf;
+		struct tm *timeInfo = localtime_r(&rawTime, &buf);
 		char timeString[10];
 		strftime(timeString, sizeof(timeString), "%H:%M:%S", timeInfo);
 		// The line below is commented for compatibility with previous