cpu/nrf51822: fixed gpio driver
boards: added LED macro for pca1000 & yunjia-nrf
core: Provide functions for different byte orders

Rationale: see #1586.
tests: Add unittests for byteorder.h
tests: fix bad copy+paste in tests-core.h
Copy some files from cpu/sam3x8e to cpu/cc2538.
Add the latest cc2538-bsl script from https://github.com/JelmerT/cc2538-bsl/commit/f3701a0
c++: core: add extern C in header files
Merge pull request #1783 from dangnhat/extern_C_in_headers_core

c++: core: add extern C in header files
Merge pull request #1699 from Kijewski/issue-1586

core: Provide functions for different byte orders
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
renamed the cpp header file to `*.hpp` to preven eventually a collision with #1789
Merge pull request #1792 from BytesGalore/rename_cpp_header_to_hpp

renamed the cpp header file from `*.h` to `*.hpp` to avoid false positive when require `extern "C"` in a C header.
make: make doc clean target ignore failures
make: add clean, distclean for RIOT

distclean
removes all build products, also depends on docclean

clean
removes all build products for the current board

also, silence clean target from Makefile.include and let it ignore errors
make: remove $(CLEANFILES), it's superfluous
udp: fix byte order in sockaddr6_t

udp_recvfrom wrote the sender port number in host byte order into the
provided sockaddr6_t. Because all send functions expect the port number
in network byte order this introduces a superfluous conversion step in
case one wants to reuse the address for replying.

closes #1406
Merge pull request #1539 from LudwigOrtmann/distclean

make: [dist]clean