Still trying to find a working script

At the moment, the setup_requires seems to work in that numpy and Cython
are built if they are not already present.  However, when the 'real'
install starts, they are missing again.

I came across the setup.py for the numexpr extension.  I think there
is a lot to potentially learn about how to do this correctly
from looking at that script.  It is nicely organized and doesn't
rely on a lot of global scope code (things are nicely organized
into functions and classes).  I think that could help as well.