Add tail_serial.

tail_serial will connect to /dev/ttyACM0 and continually stream the
serial output from the arduino.
Initial rewrite.

Use #defines for registers and add some debugging code.

Note that this is the first code to actually work properly with
regards to reading the registers.

For some, as of yet undiscovered, reason, the code will not work
unless Wire.endTransmission is called with stop=FALSE.
Add Makefile.

Why ever use a gui for programming?