Removed GPS testing code. GPS data is now sent via XBee using a specific syntax

$GPS,act,lat,lon,speed
act is A for Active and V for Void, lat and lon hold the laitude and
longitude values and have 10 decimal digits, speed has two decimal
digits and is in knots.
GPS data is now pushed through the XBee serial every 1 second via AVR interrupts

The interrupt overflow function calls the handleInterrupt method in the
Ship object.