BUILD: add _distributor_init.py to preload dll on windows

[mattip]

Part of the fix for numpy/numpy#13764, the other part (removing code from numpy/core/__init__.py and duplicating this code there) has to be done in the numpy repo after this is merged in order to reuse openblas_support.py from here.

This creates a _distributor_local.py file which is packaged with the wheel (on windows only).

I named the new file openblas_support.py in the hope that we can add some of the environment variables to it which might unify some of the travis/appveyor/future azure/ CI behaviour

[mattip]

Fixes #49

[rgommers]

This seems to do the job. One question though, why not just name this file _distributor_init.py or _distributor_init_windows.py, and just copy it into place? Seems simpler and easier to extend than this file writing from another file.

[mattip]

It seemed easier to just copy-paste the code from numpy. I also intend to extend this to handle all the OpenBlas setup (download, unzip, set up so numpy can find it) in one place rather than in each CI yaml file. This can be then reused by the numpy CI, see numpy/numpy#13772

[rgommers]

Okay thanks @mattip. You're doing the work, so let's go with your preference:)