* We have declared some functions in "timer.c" and corresponding function
* prototypes in "timer.h":
* void timer_init(void); // Initialise TCB0 to produce interrupts every 1ms
*
* Your task for Ex 9.3 is to complete the ISR declared in "timer.c" to display
* simultaneously the first digit of your student number on the LHS of the 7-segment
* display and the second digit of your student number on the RHS of this display (only
* after timer_init() is called).
*
* TIP: Every time a new interrupt occurs you should swap which digit you are displaying.
*
* TIP: You will want to declare a global or static variable so you know which digit to
* display on each iteration.
*
* TIP: You might like to refer to the following truth table for 7-segment digit mapping.
* (remember to check which output Q0..Q6 maps to which segment on the QUTy)
*
* ABCDEFG
* 0: 0000001
* 1: 1001111
