modified Makefile.include to build c and c++ in user's app
added CXX and CXXFLAGS in boards/native/Makefile.include
added test_another_mix_compiler to tests folder
added BytesGalore's test_cpp_mix to tests folder
address comment by @LudwigOrtmann - fix problem with flags for c++ by deriving from CFLAGS (removed CXXFLAGS, added CXXUWFLAGS and CXXEXFLAGS)
address comment by @LudwigOrtmann - fix source code to comply with coding conventions
address comment by @LudwigOrtmann - move applications to examples folder.