Merge pull request #3900 from haukepetersen/add_arduino_api

.gitignore

Makefile.dep

boards/stm32f4discovery/Makefile.features

boards/stm32f4discovery/include/arduino_board.h

dist/tools/arduino/pre_build.sh

doc/doxygen/riot.doxyfile

examples/arduino_hello-world/Makefile

examples/arduino_hello-world/README.md

examples/arduino_hello-world/hello-world.sketch

sys/Makefile.include

sys/arduino/Makefile

sys/arduino/Makefile.include

sys/arduino/base.cpp

sys/arduino/doc.txt

sys/arduino/include/arduino.hpp

sys/arduino/include/serialport.hpp

sys/arduino/post.snip

sys/arduino/pre.snip

sys/arduino/serialport.cpp