. SysTick.c and .h updated to handle more than one timer object
. Multiple timers are implemented as a linked list of timer objects
. Main updated to reflect new capability

*** Timer callbacks can NOT call wait() or any other functionality
    that relies on hardware interrupts such as I2C and LCD interfaces
. I2C implementation is now split in to .c and .h files
. Added #include guards to I2C.h and lcd.h
. Added I2C.c to Makefile sources list