replace openmp with thread-pool library bc openmp has larger fork boundary overhead

include/config.hpp

@@ -4,8 +4,8 @@
 #include <raylib.h>
 
 #define PRINT_TIMINGS
-// #define WEB
-#define BARNES_HUT
+// #define WEB // Disables multithreading
+#define BARNES_HUT // Use octree instead of uniform grid
 
 // Window
 constexpr int INITIAL_WIDTH = 800;