change CI from travis-ci to Github Actions (or other)

[prjemian]

There is a change in the pricing model of the continuous integration service we use to check our repository for syntax errors. By the end of the year, we will run out of free credit to use this service.

There exist many possible replacements for this service, some free, some not. One of the easiest to use is Github Actions, where the testing workflow is described in a YAML file and stored in the repo in a special directory. Here's an example: https://github.com/BCDA-APS/apstools/blob/master/.github/workflows/unit-tests-pytest.yml

These are the steps:

• setup CI process (copy from apstools and modify for our tests.
• build for these python versions ['3.5', '3.6', '3.7', '3.8', '3.9'] (drop a version of cannot construct environment)
• CI status: change the badging in the README file
• delete the travis-ci webhook

[prjemian]

Examples of CI review for the apstools project: https://github.com/BCDA-APS/apstools/actions

[prjemian]

I'll setup a CI workflow using a conda environment. We can change that to a simpler (faster) python/pip setup later, if desired.

[prjemian]

Could run the testing faster following this page: https://docs.github.com/en/free-pro-team@latest/actions/guides/building-and-testing-python#starting-with-the-python-workflow-template

Our setup is minimal. The conda tooling is not in use by all, we should test on lowest common denominator when possible.

[prjemian]

We should change the code run by

python ./utils/test_suite.py

so that it can be run by proper unit testing code, such as

pytest -vvv ./utils/test_suite.py

[prjemian]

NOTE: With conda, tests take about 5 minutes to complete.