Reorganize azure testing

[ahartikainen]

Description

Implements all the tests and builds on Azure. Removes Travis. Fixes #1061 and fixes #1060

Python 3.6, 3.7, 3.8

• BaseTests --> Tests ArviZ based tests (stats, diagnostics, plots)
• ExternalTests --> Test external libraries (data)
• Run benchmarks --> Upload results to pipeline site

Python 3.8

• Build Docs (build only if tests are passed and on master branch)
• Build Wheel (build only if tests are passed and a tag "branch") --> upload dist folder to pipeline site --> can be download and upload with twine for pypi manually.

Changes coveralls to codecov.

Checklist

• Changes are listed in changelog

Future

We could follow benchmarks somehow, but currently they are only there so we can follow them manually.

[OriolAbril]

This is probably a good time to remove the azurepipelines-coverage file which doesn't actually do anything.

[ahartikainen]

Cool,

Still needs the docs

.azure-pipelines/azure-pipelines-docs.yml

Some fix for coverage and pytest reports.

Also reporting lint etc?

Codecov? We probably should also skip tests folder from coverage.

I dropped some tests (saving external file)

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@3c2bd28). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1080   +/-   ##
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  Coverage          ?   91.61%           
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  Files             ?       93           
  Lines             ?     8704           
  Branches          ?        0           
=========================================
  Hits              ?     7974           
  Misses            ?      730           
  Partials          ?        0

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[canyon289]

I am very late to this PR but just wanted to say the work here looks great! Was looking at the testing now and everything is much better