Make Python 3.7 non-support explicit.

[montebhoover]

Fixes #20 .

[stevengum]

@montebhoover What is in your team's plan around support for 3.7? The BotBuilder SDK team is considering moving to Python 3.7 from 3.6; we'd like to be able to run with NimbusML out of the box, should customers decide to use the two together.

DCR: Target Python 3.7 instead of Python 3.6 for BotBuilder-Python [microsoft/botframework-sdk#5112]

[montebhoover]

@GalOshri The BotBuilder SDK team was asking where NimbusML support for python 3.7 falls on our roadmap for use in their planning.

[amueller]

awww. What's the issue?

[montebhoover]

@xadupre I think you explored this a while back - do you have a guess on how much time it would take to get NimbusML supporting Python 3.7?

[amueller]

I should probably have asked on #37, sorry. 3.7 is the current version of Python and not supporting it seems a major drawback. The other thread mentions major problems with 3.7. Can you elaborate? I have not heard about any issues with 3.7 so far and we had not issue supporting it in sklearn.

[xadupre]

I created a branch where I made the necessary changes to compile nimbusml for python3.7 on windows. linux and mac are easy to add but I could not test them (just need to modify csproj and sln files).

https://github.com/Microsoft/NimbusML/tree/py37_11

But:

• I did not want to build with boostpython as it seemed complex to retrieve the necessary binaries, I replaced it with pybind11.
• I used the python standard distribution instead of anaconda (that should not change anything).
• I did not run the whole test series (but so far no issues for the examples I tried)
• The build is not yet finalized as I had to copy ml.net binaries myself to .internal.libs

Conclusion:

• It is almost done.
• CI and build must be completed.
• I can share the wheel I built on Windows based on the branch mentioned above.