Cythonize files automatically in setup.py

this pull requests implements the SciPy method for dealing with cython files.  setup.py uses a system command to call the script cythonize.py which loops through all the files in the pele/ directory cythonizing every .pyx file.  It records the hash of the .pyx file in cythonize.dat and only re-cythonizes files when they have changed.

.pyx files that need to be turned into c++ files must have a line like

    # distutils: language = C++

near the top of the file.  The new auto-generated c++ files have extension .cxx

This pull requests removes all cython auto-generated c and c++ files from the repository.