** Add simulation context (VerilatedContext) to allow multiple fully independent
models to be in the same process. Please see the updated examples.
** Add context->time() and context->timeInc() API calls, to set simulation time.
These now are recommended in place of the legacy sc_time_stamp().
This patch normalizes what the tests do before exiting. After this
change each test should call final on the top module and explicitly
free the top module object before exiting.
