simulator: Add position to datalog.out

Cleanup datalog output a bit.
  * Add close/flush on exit in case we have pending data
  * Use hash for comment characters to be compatible with gnuplot
  * Report x/y/z/e position in array
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.
Add gnuplot script to explore simulator output

research/datalog.plot is a gnuplot script to plot pin outputs like
a logic analyzer and x/y/z positions as well. It's quite rudimentary
but it does recognize some keyboard commands to pan and zoom.

Be careful with keyboard repeat getting too far ahead of you.