define preprocessor variable NDEBUG=1, when CMAKE_BUILD_TYPE is not
Debug (cause issue #20)
fix overflowing buffer in test_message.cpp with strcpy.
strcpy also copied terminating '\0', which lead to length 13 (buffer
overflow) and failiure of nnxx_check() in test_message.cpp, l. 49
simplify detection of test case locations in CMake
more convenient output directory locations for CMake builds
NDEBUG=1, when CMAKE_BUILD_TYPE is not Debug (cause issue #20)