Added "printf" debug capability with inter-task safeguards in place.
Added explicit initialization of uart write protection mutex, which no only adds to readability, but also shrinks flash by 8 bytes as compared to implicitly initialized mutex.
Moved MAX_RESPONSE_LENGTH define to header file.
...and added comms.h to comms.c, otherwise that include is undefined.
Merge pull request #41 from raivisr/master

uart_printf made usable from all over the code