This allows high-level library classes to implement enhanced simulation
support even if no low-level corresponding simulation library exists, and
avoids the need for bit-banging complex interfaces like SPI or CAN.
Default behavior is still to run the robot main loop in the main thread.
The ability to run the robot main loop in a separate thread and add a hook
for running a different function in the main thread is needed for simulation
GUI support on some platforms.
