start to add a CMakeLists.txt that can build the cython .so files
it works with a library now
add potentials/_pele.so to CMake build
add a cmake function to build the library automatically
add file to setup cython libraries with cmake
add -j flag to setup_with_cmake.py

This gets passed to cmake to enable parallel build.  It does not show up
the the help messge yet
the include paths are now automatically passed to cmake
Merge pull request #83 from js850/cmake_build

add an alternate setup file which builds the cxx extensions entirely with cmake