add GitHub Actions for CI tests

[msimerson]

Why add GitHub Actions support?

• I contributed the Travis CI to this repo.
• Travis CI test execution times have increased sharply in the past months
• execution time for Travis CI on this PR: 50 seconds, wall clock duration 1 min 45 sec
• execution time for GitHub Actions on this PR: 9 seconds.
• see the GitHub results under the Actions tab in my fork
• adds tests on Windows platform
• Travis is still enabled. I recommend using them both for now, until you see how dog slow Travis is, trust that GitHub Actions is serving the same good purpose, and finally delete .travis.yml.

[msimerson]

ping

[whitequark]

Is there any point in testing on Windows? LGTM otherwise.

[msimerson]

I can confirm that at least one project that depends on this runs on Windows (as well). Node supports it well so testing just helps prevent inadvertent and easily solvable problems from sneaking in.

[whitequark]

Thanks!