Add windows-curses for support on windows

[ltalirz]

Fixes #1100.

• Building on Add windows-curses dependency for Windows #1134 to add windows-curses dependency for support on windows
• switch CI from travis to github actions, splitting different python versions into separate jobs (complete test suite run now takes <2 mins)
• add CI runs on windows and macos
• fix MANIFEST.in

See windows build at https://github.com/ltalirz/circus/runs/955260205

[ltalirz]

@biozz The new CI test environment is now set up, but this is still a work in progress:

• 3 tests on macos are failing
• tests on windows "pass" but only because all tests are being skipped ;-)

Would you mind taking it from here?
I'll give you write access to my fork (otherwise, feel free to pull my branch and make a new PR).

[biozz]

@ltalirz sure, thank you for the kick-start!

The config looks simple and easy to understand, the most difficult part will be to fix tests. And if anything goes south we can split it into several parts.

I actually would prefer to have separate PRs for github actions and windows-related fixes. But that's okay, we can keep it as is.

[ltalirz]

I actually would prefer to have separate PRs for github actions and windows-related fixes

I got the feeling as well after making the change.
I think it would probably be ok to merge the PR as-is (with the windows/macos builds failing).

If you think it's important to disable them until the tests pass, let me know and I can modify it @k4nar

[biozz]

@ltalirz well if we both agree that this PR has too much going on, could you please submit a separate one with proper branch name, topic and description? (it is ok to skip win and mac tests)

No offense, but I am all about clean commit history. I can take over if that is too much to ask.

[ltalirz]

Sure, here's a new one #1137