Create symbolic links to the game resources when building out of the CMAKE_SOURCE_DIR (fixes #121)
This is done both on Linux and on Windows (unless it is older than Windows Vista)
Also replace CMAKE_CURRENT_BINARY_DIR by CMAKE_BINARY_DIR (we have only one CMakeLists.txt)
Merge pull request #206 from akien-mga/linux-install

Make it possible to run the game out of the source dir