Borg: use appveyor.com for windows based testing

[ThomasWaldmann]

We maybe could use this service to automate testing on Windows.

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:moneybag: there is a bounty for this

[ThomasWaldmann]

I would appreciate if a Windows based developer implements this, tests it with appveyor.com and does a PR.

I created a bounty for this there:

https://www.bountysource.com/issues/26292300-use-appveyor-com-for-windows-based-testing

[RonnyPfannschmidt]

you can also use appveyor to upload windows wheels after the tests

[PlasmaPower]

Cygwin is installed to C:\cygwin and C:\cygwin64 on appveyor by default: https://www.appveyor.com/docs/installed-software#mingw-msys-cygwin

[Anakonda]

See #1240

[ThomasWaldmann]

@Anakonda can you make it do some tests?

Doesn't need to be all of them, but so we can close this issue.

[Anakonda]

I actuall have that already. I'm still trying to fix some more tests.
======= 50 failed, 427 passed, 258 skipped, 3 xfailed in 443.28 seconds =======

[Anakonda]

1307 merged, Close this now?

[ThomasWaldmann]

@Anakonda don't forget to claim the bounty.