https://coliru.stacked-crooked.com
http://www.cplusplus.com/reference/queue/queue/
https://www.geeksforgeeks.org/queue-cpp-stl/
https://stackoverflow.com/questions/1008019/c-singleton-design-pattern
https://stackoverflow.com/questions/86582/singleton-how-should-it-be-used
https://github.com/i8degrees/nomlib/blob/dev/include/nomlib/math/Rect.hpp
http://www.cplusplus.com/doc/tutorial/namespaces/
https://www.moderncplusplus.com/map/
https://stackoverflow.com/questions/26281979/c-loop-through-map
https://thispointer.com/stdmap-tutorial-part-1-usage-detail-with-examples/
https://www.guru99.com/best-cpp-books.html
http://vinniefalco.github.io/LuaBridge/Manual.html#s4.1