added microcontroller submodule

this submodule contains the code that runs on the microcontrollers
added LED microcontroller interface
tweaked debugging interface to use new 2's complement thruster commands, also updated microcontroller submodule

submodule is updated with new ported version of code, plus the new 2's complement thruster commands
Merge remote-tracking branch 'origin/user/irwinj' into dev-integration
tweaked old sub's interface to use 2's complement thruster commands
Merge branch 'user/irwinj' of https://github.com/PalouseRobosub/robosub into dev-integration