EME Conformance Harness

We assume the eme-go from rfjakob to be correct (as we need it for gocryptfs) but we need a web impl.

While the TS-version maintainer said they ported all test cases, we instead want to "fuzz-test" it

Since we trust the go version, we only need go -> TS

1. gen.go throws in test cases into the trusted go impl and generates vectors.json
2. The typescript mocha harness loads vectors.json, reruns it through the TS impl and does byte4byte equality checks

Looks all fine, TS library seems to be identical