CI: add build jobs for macOS and Windows in travis.yml

[fkuehlein]

I will have to do this step-wise to see what works, as Travis CI documentation does not really cover our specific case. Will start with the macOS job, add a Windows job after that, and finally add the Linux jobs back again, hopefully not needing too many builds along the way.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9779716) 60.72% compared to head (138a445) 60.72%.
Report is 2 commits behind head on master.

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  Misses       2497     2497           

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[fkuehlein]

• macOS: building successfully, although wasn't yet able to combine with the linux jobs.

• Windows: Silent install of miniconda.exe is not working somehow, just timing out.
  Tried going with choco install miniconda3 instead, but cannot find conda command afterwards. Maybe /AddToPath not working? Package does not appear to be maintained ...

  Will probably just go with choco install python instead.

[fkuehlein]

This PR is becoming a bit of a mess, but I've run into multiple issues here. @ntfrgl, sorry for bothering you with it at this stage, but maybe you have a quick idea on what direction to proceed? I feel like I'm acting pretty clumsy on this, have no experience whatsoever with windows and/or git bash, don't want to waste too much time and credits...

Relevant parts of Travis docs including examples: explicitly including jobs into build matrix, run travis on multiple os, the windows build environment

i. combining the linux and macos jobs

macOS builds are running fine, although taking about 20 minutes which could be sped up maybe. Only I could not figure out how to expand the linux build matrix with a single macOS build (see 5145e49 for my most recent try). Therefore, in f66d3e3 I just added all linux jobs explicitly, which is not very elegant but works.

ii. installing miniconda on windows vm

I tried installing miniconda two ways:

• download the .exe file with wget or curl and do a silent install (/S flag) (see 36c107e and fe538c9) as proposed by Anaconda docs:

  $> curl https://repo.anaconda.com/miniconda/Miniconda3-latest-Windows-x86_64.exe -o miniconda.exe
  $> start /wait "" miniconda.exe /S

  Problem is the build will just time out with no response after 10m. I tried the same in cmd.exe on a Windows machine and it finished within a minute. Seems to me that the second command is run before the first one is finished and thus will never succeed (see build logs).

• install via chocolatey:

  $> choco install miniconda3 --params="'/S /InstallationType=JustMe /AddToPath=1 /D=%UserProfile%\miniconda'"

  Problem is it won't find the conda command after that (see 46615ec), although the /AddToPath flag is set. Probably need to refresh environment variables but refreshenv command is not found either (see 8db98d0).

now an alternative would be to go without conda and just pip instead, of course, but would then need to rewrite the everything for just the windows case.

[fkuehlein]

Finally got the choco install miniconda3 to run in 7698e85 thanks to an example found here.

Now pyunicorn will install fine, but when trying to run tests I get this error from matplotlib.font_manager when importing igraph:

..\..\..\miniconda\envs\test-env\lib\site-packages\matplotlib\font_manager.py:215: in win32FontDirectory
    return os.path.join(os.environ['WINDIR'], 'Fonts')
..\..\..\miniconda\envs\test-env\lib\os.py:679: in __getitem__
    raise KeyError(key) from None
E   KeyError: 'WINDIR'

see build log for full error message. I checked for the $WINDIR environment variable in 147a406 and it is correctly set (see build log), don't understand why matplotlib won't find it and hence giving up for today. Don't think installing miniconda via choco is optimal anyway because it is limited to python=3.9 and does not appear to be maintained ...

[fkuehlein]

Same problem occurs without conda, just using pip (see commit above).

[ntfrgl]

@fkuehlein, thank you for getting all the tedious work done! This is a big step forward for the project.

In my commits above, I resolved the remaining issues you mentioned, and achieved some simple speedups.

[fkuehlein]

Thank you lots, @ntfrgl! Great to see all green checks on this ... with the travis.yml containing everything we need yet being boiled down to improved readability and fair speed, I'll merge this right away. :)