Update example code to use write_all_buf (#408)

use aws_types::region::{EnvironmentProvider, ProvideRegion};

use bytes::Buf;

use structopt::StructOpt;

use tokio::io::AsyncWriteExt;

use tracing_subscriber::fmt::format::FmtSpan;

    let mut file = tokio::fs::File::create(out_file)

        .await

        .expect("failed to create file");

    while blob.has_remaining() {

        file.write_buf(&mut blob)

    file.write_all_buf(&mut blob)

        .await

        .expect("failed to write to file");

}

}

[dev-dependencies]

proptest = "1"

base64 = "0.13.0"

tokio = { version = "1", features = ["macros", "rt", "fs", "io-util"]}

tokio = {version = "1.6", features = ["macros", "rt", "fs", "io-util"]}

tokio-stream = "0.1.5"

//!

//! ### Writing a ByteStream into a file:

//! ```rust

//! use bytes::Buf;

//! use smithy_http::byte_stream::ByteStream;

//! use std::error::Error;

//! use tokio::fs::File;

//! ) -> Result<(), Box<dyn Error + Send + Sync>> {

//!     let mut buf = output.audio_stream.collect().await?;

//!     let mut file = File::open("audio.mp3").await?;

//!     while buf.has_remaining() {

//!         file.write_buf(&mut buf).await?;

//!     }

//!     file.write_all_buf(&mut buf).await?;

//!     Ok(())

//! }

//! ```