matt.broadstone@mongodb.com points out that the advanced functionality of a Targeter is often not needed when sending an RPC request, because a default of ReadPreference "primary" is almost always what users want. In such cases, a URI (or even shard ID) is sufficient to target the RPC request. Let's add and document an overload that takes a URI and/or shardID instead of a Targeter, so that users don't need to manage additional state/complexity in the "easy" case.