yourlogarithm has created PR #1108: Macro for field projection proposal in mongo-rust-driver

Issue Text:
Usage example

```bash
cargo add mongodb -F projection_macro
```

```rust
use mongodb::options::

{FindOptions, Project}

;
use serde::Deserialize;

#[derive(Project, Deserialize)]
struct Person

{ #[serde(rename = "n")] name: String, age: u8, male: bool, #[serde(rename = "h.a")] address: String, }

#[tokio::main]
async fn main() {
let client = mongodb::Client::with_uri_str("mongodb://localhost:27017").await.unwrap();
let projection = Person::project().name().age().address().build();
println!("{:?}", projection); // mongodb::bson::Document(

{"n": Int32(1), "age": Int32(1), "h.a": Int32(1)}

)
let options = FindOptions::builder().projection(projection).build();
let document = client.database("test").collection("people").find_one(None, options).unwrap().unwrap();
}
```