Adapt to changed terminology for master/replica

[mp911de]

We should reflect these changes in Lettuce, see https://github.com/antirez/redis/issues/5335.
This requires changes in:

• Commands (REPLICAOF)
• Command keywords (REPLICAS)
• ReadFrom
• MasterReplica (previously MasterSlave)
• Documentation

[mp911de]

Roadmap:

• Documentation – 5.1
• Non-public API changes (internal API/non-breaking) changes – 5.2
• Introduce methods and types with new terminology – 5.2
• Deprecate Public API with deprecated terminology – 5.2
• Public API changes (breaking changes) – 6.0

[mp911de]

With Lettuce 6 we should move the majority of the MasterSlave API to a new package and leave only the deprecated public API entry points to i.l.c.m.MasteSlave in the current package.

This requires deprecation of all public API artifacts in the current masterslave package.