added board airfy beacon

wiki page: https://github.com/RIOT-OS/RIOT/wiki/Board%3A-Airfy-Beacon

for interrupt driven UART: https://github.com/RIOT-OS/RIOT/pull/1555
for working timers: https://github.com/RIOT-OS/RIOT/pull/1824 and https://github.com/RIOT-OS/RIOT/pull/1827
see above