support CMAKE_<LANG>_... variables

#197 , solve the LANG issue first,

the PROJECT is harder, will solve it later after this pull request.
10 minutes are reasonable time, C++ coding is tiresome, I usually take much more than 10 minutes before switching project,

it's impossible for a C++ developer to switch project and edit *CMakeLists.txt* in ten minutes. Usual pattern is to tweak CMakeLists.txt, compile, modify some C++ code, re-complile, debug, any operation after editing CMakeLists.txt will surely take much more than 10 minutes.