Get and batch get support

use firestore::*;
use futures::stream::BoxStream;
use serde::{Deserialize, Serialize};
#[derive(Debug, Clone, Deserialize, Serialize)]
struct MyTestStructure {
    some_id: String,
}
const TEST_COLLECTION_NAME: &str = "test";
async fn example(db: FirestoreDb, my_struct: MyTestStructure) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
let find_it_again: Option<MyTestStructure> = db
    .fluent()
    .select()
    .by_id_in(TEST_COLLECTION_NAME)
    .obj()
    .one(&my_struct.some_id)
    .await?;

let object_stream: BoxStream<(String, Option<MyTestStructure>)> = db
    .fluent()
    .select()
    .by_id_in(TEST_COLLECTION_NAME)
    .obj()
    .batch(vec!["test-0", "test-5"])
    .await?;
Ok(())
}