cpu/stm32f4: optimized GPIO driver implementation
SQUASH: cpu: fixed some typos
SQUASH: cpu/f4: changed order of irq enabling seq
cpu/nrf51822: added HFCLK initialization
boards: added CLOCK defines to NRF based boards
Adapt start page to improve developement procedures
boards/samr21-xpro: declare implemented features
cpu/cc2538: made _kill(_r) syscalls weak
board/openmote: enabled C++ support
board/cc2538dk: enabled C++ support
tools/licenses: add 3c-BSD-atmel3 pattern
tools/licenses: add 3c-BSD-nordic pattern
license: added missing license for msp430 time.h
tools/licenses: remove unused 3c-BSD-clark
cpu/board: update stale redbee license headers
tools/licenses: add 1c-BSD-stanford pattern
drivers/cc2420: use DEBUG_ENABLED instead of DEBUG

compare https://github.com/RIOT-OS/RIOT/issues/2067
nrf51: halt works better
Merge pull request #2065 from LudwigOrtmann/issue-392

license header + pattern cleanup
add hdc1000 sensor driver