Transition to GitHub Workflows

[jcfr]

Continuous integration for Linux, macOS and Windows is implemented using 3 different services requiring three different configuration files:

appveyor.yml
circleci/config.ym
.travis.yml

To simplify and streamline maintenance, CI configuration should be transitioning to using GitHub workflow and instead have files common to all platform (e.g .github/workflows/build-test-package.yml)

Experiment to elaborate a working approaches are being done here: jcfr/ci-sandbox#9