Merge pull request #2 from bfroehle/so_ext

Use distutils to determine the compiled extension module extension.
Python 3 support.

The current method of compiling, i.e., by calling f2py directly, only
works if the current Python interpreter is in the #! line of the f2py
script. Better would be to call `[sys.executable, 'f2py', ...]`, however
we can avoid all of this by mimicking the `f2py` script directly.

Here we directly call the numpy.f2py.f2py2e.run_compile() entry point,
after some small amount of setup to get sys.argv and the current working
directory set appropriately.