working multithreading

finally managed to multithread folder scanner and rtp. it may still have some bugs. but it works

src/client_backend/md5hash.h

@@ -4,4 +4,6 @@
 #include <iostream>
 #include <fstream>
 #include <string>
-int md5_file(const char* path, char* md5Hash);
+int md5_file(const char* path, char* md5Hash);
+//char* md5_file_t(const char* path_);
+std::string md5_file_t(const std::string& path_);