We are now using the Mega

This will resolve the memory issues since the Uno only has 2k SRAM
and the Mega has 8k with the same wordsize. Its a shame that you
have to get all these extra IO pins on the Mega when we really only
needed the extra RAM but it works.
Found better values

Found better values for the correction algo. The mouse now goes
straight pretty much all the time. Will need to tweak it just a
little to get it perfect.
Found better values for turns and block size

The mouse now turns more accurately and does not active the safety
cutoff as much.
Added debug statements and fixed nav_drive_to_target()

Added debug statements so we can see what is going on in the code.
Also use the buffer that is passed in to nav_drive_to_target()
instead of creating our own.
Make datatype more explict
Implement multiple targets

Now the mouse has multiple targets for testing purposes. We will
never use it in the competition but it is nice to showoff in the
window of robotics.