Retired some TODOs.  Documented Z motor variables.
Removed extraneous VPATH.
Comment and shell quoting.
Serial port now uses weird flow control.
The cat test tests serial I/O in several ways.  Not well packaged yet.
Rough draft of ideas to simplify makefiles.
Ignore core, thruport executable, cat/feeder executable.
Added: baud rate.  Completed: V-wheel spacers.
Added a.out and core to clean rules.
First draft of thruport, the USB serial port daemon.