cpu/nrf51822: fixed gpio driver
boards: added LED macro for pca1000 & yunjia-nrf
at86rf231: replace vtimer_usleep by hwtimer_wait

This fixes a bug where the callback to unlock the thread, put to sleep by
`vtimer_usleep` wouldn't be woken up due to overhead. Using hwtimer_wait
works for now, but this section will be replaced a driver refactor anyway.
cpu/stm32f1:board/iot-lab_M3: fix and cleanup for GPIO low level driver
cpu/stm32f1: overwrite HWTIMER_WAIT_OVERHEAD
Merge pull request #1720 from haukepetersen/fix_nrf_gpio

cpu/nrf51822: fixed gpio driver
Merge pull request #1722 from haukepetersen/fix_nrf_leds

boards: added LED macro for pca1000 & yunjia-nrf
Merge pull request #1756 from thomaseichinger/welq-fix

cpu/stm32f: boards/iot-lab_M3: cleanup and fixes