Query deserializer feature

[Dushistov]

It would be nice to have optional functionality to decode query as whole,
example:

while let Some(item) = query_iter.next()? {
    let (p1, p2, ...): (T1, T2, ...) = deserialize_with_serde(item)?;
}
#[derive(Deserialize)]
struct QueryResult {
   f1: T1,
   f2: T2,
...
}
while let Some(item) = query_iter.next()? {
    let res: QueryResult = deserialize_with_serde(item)?;
}

[Dushistov]

Initial implementation can be found here: #66 .
What missed:

• tests
• feature to make it optional
• replace bunch of todo! with help of usage of serde-fleece