Add linting and tests to Github Actions

[peterldowns]

While I was working on https://github.com/rubenv/sql-migrate/pull/242 I was surprised to find a lack of automated testing. If you'd like, this PR sets up CI on Github Actions and adds some linting rules, too. I think switching to Github Actions will make it easier for people to contribute and make sure they're not breaking anything, especially for older versions of golang. Hopefully it will make your life easier as a maintainer, too.

If you are not interested, no problem, please feel free to close the PR.

• Adds a Makefile with rules for make lint, make test, and make build
• Adds golangci-lint as a linter, with explicit configuration
• Replaces the .travis.yml CI configuration with Github Actions
  • Runs go build and go test for golang version 1.13-1.20
  • Runs golangci-lint and go mod tidy and makes sure there were not any changes detected
  • Runs the integration tests for golang versions 1.13-1.20
• Fixes building/installing on go < 1.17
  • https://github.com/rubenv/sql-migrate/commit/4e43feaed0a6db1c7140ff655d6ecb39b2b01a88 broke compatibility through a transient dependency on golang.org/x/sys, which as of recent versions uses unsafe.Slice which was introduced with go1.17.
• Fixes all linter errors

[peterldowns]

You can see an example run of the proposed workflows here, on this PR (same branch, just opened as a PR against my fork so that the workflow has permissions to run) https://github.com/peterldowns/sql-migrate/pull/1

https://github.com/peterldowns/sql-migrate/actions/runs/5136897251

[rubenv]

Oh thank you very much!

Once Travis died I never got round to properly adding CI again. This is great.

[peterldowns]

@rubenv you're welcome, I'm happy that I was able to contribute something useful :) If you run into any problems with it, please just tag me or send me an email and I can try to help out.