Using clang-tidy's `modernize-use-nullptr`. https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-nullptr.html
List of changes: - Modified bvh class to handle 2D and 3D as a template - Changes in Rect2, Vector2, Vector3 interface to uniformize template calls - New option in Project Settings to enable BVH for 2D Physics (enabled by default like in 3D)