Update CI

[SemyonSinchenko]

• run tests on pull-requests (for some reason they are not running at the moment);
• switch from ludicsoftware to scalameta;
• update/revisit plugins
• build scaldocs and deploy to GH pages (Add Laika and API docs #134)
• publish sources (Publish sources #46)

Maybe something else?

[zeotuan]

Let me dig up why this is happening. It's actually running on my fork but my fork has accumulated quite some changes.

[zeotuan]

oh actually it just started running on #131

[SemyonSinchenko]

@zeotuan PRs from first-time contributors requires an approve from maintainers, I think that is the reason.

[SemyonSinchenko]

Feel free to ping me, I will approve runs