Compiler for pyx generated C

[alex.pi...@gmail.com]

We (qutip.org) have been using your package (from conda-forge) for quite a while. 

Basically it seems to work, and the 'mingw' from conda defaults does not (hangs on "searching for Python27.dll")

Recently we started getting this warning after compiling with compiler=mingw32 and calling pyximport

```

"unknown conversion type 'z' in format"

```

It seems a whole host of other people report this, with no clear solution.

I am not sure that we are using mingwpy in the right way.

Is there another option for `compiler=`

Basically we need something that has `complex.h`, which the Windows one does not.

At the moment we only support py27 and py34 on Windows. 

Clearly we would also like to support py35 ad py36.

[stone...@gmail.com]

My understanding is that there is a Microsoft Legal move in waiting since 1 year:

https://twitter.com/zooba/status/814854207295471617

And until it happens (or not), mingwpy can't progress towards python-3.5/3.6 (VS2015 compiled) compatibility

[alex.pi...@gmail.com]

Ok, many thanks for the info.

I have managed to make some progress. Installing Windows SDK v7 made the warning go away.

I believe there is some distutils patch I can apply that will mean I may be able to specify 

`compiler=mingw-w64`

or similar that may mean I am able to build 64bit extensions in Windows (for py27 and py34)