- added some comments in commands.c/h about usage of the file
- added a MAX_CONTROLLER_ID and MAX_CONTROL_VAL_ID to the enums in commands.h
- implemented cb_set_control in callbacks.c to work with the new parameter struct
- changes the parameter_struct to now contain an array of pid_controllers instead of a bunch of random PID_t members
- the new parameter_struct array can now be accessed by controller ID as defined in commands.h

Integrated changes from comm_dev (interrupt-driven UART) and updated code to work well with the new style. Compiles, but have not tested running yet.

Autonomous mode is throttle-only. Fixed bug in stringBuilder that would fail to resize byte data. Packets that don't have a matching checksum are thrown away now.