SIMULATOR has now an Attach() method, which should be called
with proper SIMULATION_MODEL that should be simulated, before calling Run()
Concrete class of SIMULATION_MODEL for ngspice is NGSPICE_CIRCUIT_MODEL,
renamed from NETLIST_EXPORTER_PSPICE_SIM. DIALOG_SIM_SETTINGS relies
on above mentioned object, so it was added as an argument of the constructor.
One cannot call ngSpice_Init() twice without unloading the dll. When calling
ngSpice_Init, we pass a pointer to a NGSPICE instance and thus it cannot be changed.
When any of the callback function is called with a stale pointer everything crashes.
Sylwester Kocjan
Wayne Stambaugh
Ian McInerney
Sylwester Kocjan
Maciej Suminski