Move CI to Github Actions

[Brenton M. Wiernik]

@retorquere Could you help to move the CI from Travis to Github actions?

[Emiliano Heyns]

Yep, no problem.

[Emiliano Heyns]

Done. The cslrun output doesn't display great, I'll look into that.

[Emiliano Heyns]

We have a decent long format and short format log option. I generally go for the more chatty versions, but the short version is easier for a glance status.

[Brenton M. Wiernik]

I don't have a strong preference

[Emiliano Heyns]

OK, committed on master. I've also removed the travis spec.

[Brenton M. Wiernik]

Thank you!