New setup.py build system

Replace "OpenSSL The Setup Script" with refactored version using custom distutils commands.  Move api_gen, config.pxi and Cythonizing into a build_ext replacement, and ``-hdf5``, ``--mpi``, etc., into a new command "configure".

Remove the flaky ``setup_requires`` and replace with ``install_requires``, which allows ``pip install`` to succeed even in a new virtualenv without NumPy or Cython installed.

Use of environment variables (``HDF5_DIR``, ``HDF5_VERSION``) is unchanged.