Implement the top-level game loop

[Adnn]

Should un-couple simulation update steps from frame rendering:

• [x] rendering to a higher frequency than simulation

  • [x] Should also support the opposite (e.g 100hz simu on 60hz VSynced screen)

• [x] Make sure it cannot spiral to death (an update too long, so next dT is longer, so update is even longer, etc...) (can use an upper limit "frame time delta", but beware of the case where RenderRate < SimuRate, where it is normal that a frame time might be several update periods).

• [x] Ability to submit primitives/commands to the GPU for frame N while starting simulation update for frame N+1

[Adnn]

Spiraling to death is naturally avoided by the fixed simulation delta.

Submitting commands for frame N while simulating frame N+1 is a natural feature of the multithreaded model.