Continuous integration setup

[SupraSummus]

I've been working with the NBT repo and noticed there's no CI running. Last report from coveralls was way back in 2015 and there's no green checkmark to show tests are passing.

Having a CI is pretty important for maintaining project quality. It looks like the current Travis CI setup might be disabled or out of credits.

Could we get a CI setup going again? Doesn't have to be Travis, GitHub Actions or something else would work too. I can help to set it up. In fact I think trying out GH actions at my fork will be my fun for the evening, cheers!

[SupraSummus]

I wonder if we should delete the Travis CI config from the repo to avoid confusion of future contributors? They may base their decisions and understanding on this outdated config. I think it is better to remove it.