Replace travis with github actions

[nerzhul]

Travis is quite old, slow and unfriendly to maintain. Use the new github
actions for some of our checks instead of travis.

This speeds up the build, github infra is faster, and also maintained, unlike travis old runners :(

This should permit in the future to restore the Mac OSX build and maybe windows native builds

To do

This PR is a Ready for Review but there is a missing build

• Windows binary builds

How to test

Just look at the ci ?

[nerzhul]

travis is totally broken currently... Nice haha

[sfan5]

I don't think there's a pressing need to move to Github actions, having all checks on a single platform is quite nice. On the other hand travis is quite slow sometimes and this can speed it up.

I'm neutral to this. Would be nice to hear other coredevs opinion on this.

[BuckarooBanzay]

@nerzhul Interesting, what about integration-tests to verify that the final build actually runs?
I'm using this pattern for quite a while in my mods and tools now:

• Example Action: https://github.com/blockexchange/blockexchange/blob/master/.github/workflows/integration-test.yml
• Test script: https://github.com/blockexchange/blockexchange/blob/master/test/integration-test-standalone.sh

Also here for my custom minetest build:

• Action: https://github.com/pandorabox-io/minetest_docker/blob/master/.github/workflows/docker.yml
• Integration-Test script: https://github.com/pandorabox-io/minetest_docker/blob/master/test.sh

This spins up the built binary and does some (currently stupid) sanity checks on that..
You could even test mapgen related functions (https://github.com/mt-mods/jumpdrive/blob/master/integration_test.lua)

[nerzhul]

It will be the same as before currently, i just want to have iso builds, but after we can have PR to improve that. Don't forget that gitlab does the artifact build

[nerzhul]

@sfan5 your turn