Preliminary support for Python 3.8

[tmontes]

• Python 3.8b4 is out (and 3.8.0, as of this update!).
• Tests pass on local macOS dev system.
• Let's:
  • Add that to Travis CI, testing on Linux. (failed horribly in Initial CI work to support Python 3.8 #118)
  • Add 3.8.0 to Azure Pipelines, testing on Windows and macOS.
  • Include Linux testing on Azure Pipelines.

[tmontes]

PROGRESS:

• Had difficulties in getting Travis CI to work.
• Moved every test to Azure Pipelines.