Added useful functions to CMakeLists.txt

The added functions were:
* use_cxx11( target )
      Configures the compiler to enable compilation of C++11.
* trillek_executable( name file1 file2 ... fileN )
      Same as add_executable, except with C++11 enabled by default.
* trillek_test( name file1 file2 ... fileN )
      Same as trillek_executable, except with googletest automatically linked
      in, the googletest include files added to the include path and then
      added to the CMake test suite.