use tap instead of ava, 100% test coverage, move types to types folder, activate linting in ci-pipeline

[Uzlopak]

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Fdawgs]

Don't know enough about tap to approve that bit, but the rest LGTM.

[Uzlopak]

The only big change of the tap conversion was that ava has this test.serial.cb functionality, which basically spawns a new process for the unit test. This is relevant because we are listening in those two tests on process-events. If the tests run in parallel, then the tests fail, because we are listening on all events.

Tap does not have this convenient way to run subtests in an own process. But you just have to extract the subtest to a separate suite and it runs in a separate process.

[mcollina]

lgtm