Compatibility tests

[alisaifee]

I've added a couple of integration tests in the CI for https://github.com/alisaifee/coredis at the moment covering:

• string operations
• hash operations
• list operations
• set operations
• sorted set operations

You can see them here for example.

I'll add pubsub once the resolution to #111 is available.

Would it be useful to reference this somewhere in the documentation?

[romange]

Definitely. We have "API readiness doc" linked from README.
We could put the reference there, before all the APIs expansions.