Serial communication from diveSim to unoDiveComp

Added code to unoDiveComp.py to accept depths over serial, if the
macro SERIAL_DEBUG has been defined.

Added code to diveSim.py to read the current depth over serial to the
unoDiveComp.

Todo:
* Pass current date and time over serial
* Handle dive time correctly on unoDiveComp
Serial passing of UTC

diveSim.py now passes (and unoDiveComp now accepts) the current time
in UTC over serial.