integer-encoding 4.1.0

varint+zigzag and fixedint integer encoding/decoding (https://developers.google.com/protocol-buffers/docs/encoding)
Documentation 
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use std::fs;
use std::io;

use integer_encoding::*;

async fn write_test_files() -> io::Result<()> {
    let _ = fs::remove_file("/tmp/varintbytes");
    let mut f = tokio::fs::File::create("/tmp/varintbytes").await?;
    f.write_varint_async(30 as u32).await?;
    f.write_varint_async(60 as u32).await?;
    f.write_varint_async(90 as u32).await?;
    f.write_varint_async(9000000 as u32).await?;

    let _ = fs::remove_file("/tmp/fixedintbytes");
    let mut f = tokio::fs::File::create("/tmp/fixedintbytes").await?;
    f.write_fixedint_async(30 as u32).await?;
    f.write_fixedint_async(60 as u32).await?;
    f.write_fixedint_async(90 as u32).await?;
    f.write_fixedint_async(9000000 as u32).await?;
    Ok(())
}

async fn read_and_verify_varints() -> io::Result<()> {
    let f = tokio::fs::File::open("/tmp/varintbytes").await?;
    let mut f = tokio::io::BufReader::new(f);
    let i1: u32 = f.read_varint_async().await?;
    let i2: u32 = f.read_varint_async().await?;
    let i3: u32 = f.read_varint_async().await?;
    let i4: u32 = f.read_varint_async().await?;
    assert!(f.read_varint_async::<u32>().await.is_err());
    println!("{:?}", (i1, i2, i3, i4));
    assert!(i2 == 2 * i1 && i3 == 3 * i1);
    Ok(())
}

async fn read_and_verify_fixedints() -> io::Result<()> {
    let f = tokio::fs::File::open("/tmp/fixedintbytes").await?;
    let mut f = tokio::io::BufReader::new(f);
    let i1: u32 = f.read_fixedint_async().await?;
    let i2: u32 = f.read_fixedint_async().await?;
    let i3: u32 = f.read_fixedint_async().await?;
    let i4: u32 = f.read_fixedint_async().await?;
    assert!(f.read_fixedint_async::<u32>().await.is_err());
    println!("{:?}", (i1, i2, i3, i4));
    assert!(i2 == 2 * i1 && i3 == 3 * i1);
    Ok(())
}

#[tokio::main]
async fn main() {
    write_test_files().await.unwrap();

    read_and_verify_varints().await.unwrap();
    read_and_verify_fixedints().await.unwrap();
}