Implements discoveryKey from hypercore-crypto

[bltavares]

Choose one: 🙋 feature

Checklist

• [x] tests pass
• [x] tests and/or benchmarks are included
• [x] documentation is changed or added

Context

This commit implements the discoveryKey code from hypercore-crypto.

The code was commented out, so it was more of a matter of updating it to use the appropriate functions from Blake2b, and add a test scenario.

The test scenario in use is the same one presented on https://datprotocol.github.io/how-dat-works/

Semver Changes

Minor bump

[khernyo]

Thanks!