update(ics2017-pa2.2): implement 'xchg r2a' instruction
update(ics2017-pa2.2): implement 'xchg r2a' instruction

issue sabertazimi/ics-2017#2

sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab,sabertazimi/hust-lab