Simulator: slow to 1/10th real-time

Reduce the simulated timer to 1/10 actual time.  There is no need
for the simulator to run at full speed for now, and some PCs may
not be able to attain real-time speed anyway due to PC clock
speed, scheduler slack or OS differences.

Maybe the simulated timer interrupt is not needed at all and some
cooperative timer interrupt could be used instead.  Such a setup
may even run faster as it could also run >1.0x time when there is
nothing to do.  This bears investigation later.  For now, the
simulated timer interrupt seems more realistic and possibly valuable.

simulator/timer_ext.c

@@ -9,7 +9,7 @@
 #include <stdio.h> // printf
 #include <unistd.h> // usleep
 
-#define TIME_SLOW_FACTOR 1
+#define TIME_SLOW_FACTOR 10
 
 static void schedule_timer(uint32_t useconds);