Unified return value (record + meta)

[kuy]

Actual Client::read() returns a tuple of data and meta. This is not ergonomic API. So I want to unify them and change its signature to return a single value.

Before

let (record, meta) = client.read().id("...");
println!("name={}, created={}", record.name, meta.created_on);

After

let record = client.read().id("...");
println!("name={}, created={}", record.name, record.created_on);