Set up a CI process using Github Actions

[angusmcleod]

We need to estblish a CI process for this repository using github actions. Initially this process should just run the existing unit tests on each PR, and nothing more. No additional tests or liniting to be added in this initial task, just setting up the process.

You can establish a GH Actions workflow in a PR, so technically no additional repo access is required, however that can be granted if need be.

Note: as part of this we should remove the existing Travis config. GH Actions is preferred as the complete CI solution here.

[tpltnt]

Can this be closed given that PRs #12 and #15 are merged now and the tests have been scrubbed?