Added 4 different game loops:
- runFixedDeltaTime
- runVariableDeltaTime
- runSemiFixedDeltaTime
- runFixedSimulationVariableFramerate

All timing has been ported to std::chrono in nanoseconds.

Added Integrator class which implements two different integrators:
- Euler
- RK4

Integrator class also has State and Derivative structs for physics matters.

Added statistics utilities to the Game class (fps, time per update, etc) and required resources (sansation font).