Use mt19937 random number generator instad of the default one

src/global.h

@@ -22,6 +22,8 @@
 #define NCMPCPP_GLOBAL_H
 
 #include <boost/date_time/posix_time/posix_time_types.hpp>
+#include <random>
+
 #include "mpdpp.h"
 #include "screen.h"
 
@@ -58,6 +60,9 @@ extern std::string VolumeState;
 // global timer
 extern boost::posix_time::ptime Timer;
 
+// global RNG
+extern std::mt19937 RNG;
+
 }
 
 #endif // NCMPCPP_GLOBAL_H