Initial CI work to support Python 3.8

[tmontes]

Addresses #117.

[codecov-io]

Codecov Report

Merging #118 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #118    +/-   ##
======================================
  Coverage     100%   100%            
======================================
  Files          22     18     -4     
  Lines         871    694   -177     
  Branches       56     26    -30     
======================================
- Hits          871    694   -177

Impacted Files	Coverage Δ
tests/helpers.py	100% <0%> (ø)	⬆️
tests/mixin_use_new_instance.py	100% <0%> (ø)	⬆️
tests/mixin_use_shared_instance.py	100% <0%> (ø)	⬆️
src/wires/_callable.py
src/wires/__init__.py
src/wires/_wires.py
src/wires/_shared.py

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[tmontes]

How nice of Travis (or GitHub? or both?):

• The check stalled at "Expected - Waiting for status to be reported"
  (see Travis CI reports "Expected - Waiting for status to be reported" on the GitHub Status API, but the status never arrives travis-ci/travis-ci#10204).
• Let's see if we can overcome this somehow quickly
  fiddles with a few settings @travis and with branch protection on this project

[tmontes]

PROGRESS:

• Travis migration from "webhook" to "application" is either non-trivial, or either party is acting up...
• After disabling the old "webhook" travis.org and enabling/installing the new "application" travis.com thing, Travis is complaining that it can't see this repository. :/

NEXT:

• Let's wait a while and see if there might be some kind of queued up job that will, at some point in the near future, make Travis "see" what it needs to see.
• Then, we can re-enable the branch protection to depend on Travis checks.

sigh!

[tmontes]

PROGRESS:

• Having lots of trouble making travis-ci.com see this project / migrate it from travis-ci.org.
• KISSing by running all tests on Azure Pipelines (thanks MS).

[tmontes]

NEXT:

• Without Travis, no information is being pushed to codecov.io.
• Can we make Azure Pipelines do that for us? Idea:
  • pip install codecov
  • codecov -t <codecov-side-token>