Running simualtions via step()

[ptheywood]

Most users are expected to run simulations via simulate().

Alternatively, users can use step() manually, to run simulations step by step themselves, however they must then also handle other parts of the typical simulation themselves:

• Init functions will not be executed for them. They must call CUDASimulation::initFunctions() themselves.
• Any Logging from a previous Simulate() will exist, unless they call CUDASimulation::resetLog()
• step() returns a boolean, set to true if the simulation loop is expected to continue, and false if any Exit Condition returned flamegpu::EXIT. It is up to the user to deal with this.
• The user will/may need to call processStepLog after the last step they intend to run.
• Exit functions will not be exectued for them, they must call CUDASimulation::exitFunctions().
  • Exit function logging will also need to be explicitly processed, via processExitLog
• If they wish export logs to disk, they need to call exportLog as appropriate.

I.e. they need to handle anything in simulate().

There are also several things that will not work.

• The Simulation time will not be recorded, and timing from any previous calls to simulate() on the same instance may be present / accessible.
• There is potential for bugs if anything is too strongly assuming that simulate is the only option (per step allocations perhaps)

As this is not the intended / typical way users are expected to run simulations, it should be marked as such in some way.