polish lib.rs examples

[yoshuawuyts]

This updates our lib.rs examples, showing off more of what async-std can do, and somewhat simplifying what we were already doing. Additionally it should make it nicer for people from other languages to understand what async rust is about.

Closes #522. Thanks!

Screenshots

[brandonros]

I don't know if this is sufficient to close the issue.

const main = async function () {
  const rows = await queryDatabase()
  const apiResponse = await fetchJson()
}

I think an example that showcases multiple uses of spawning tasks into something that main can then block on is much more realistic.

[ghost]

Lgtm after @k-nasa's comment on the attributes feature gets addressed.

[omac777]

Here is an example that shows passing 3 arguments within a task::block_on, 2 string arguments along with a vector of strings.
It compiles/runs successfully.

use std::env::args;
use async_std::fs::File;
use async_std::io::{self, BufReader};
use async_std::prelude::*;
use async_std::task;

async fn say_hi( mypath1_ : &str, mypath2_ : &str, myFilePaths_ : &mut Vec<String>) -> io::Result<()> {
   
    task::block_on(async {
        println!("mypath1_:<<{}>>",mypath1_);
        println!("mypath2_:<<{}>>",mypath2_);
        for oneFilePath2 in myFilePaths_ {
            println!("oneFilePath2:<<{}>>", oneFilePath2);
        }

        Ok(())
    })    
}

fn main() -> io::Result<()> {
    let path1 = args().nth(1).expect("missing path argument");
    let path2 = args().nth(2).expect("missing path argument");

    let mut vsMyFilePaths : Vec<String> = Vec::new();
    vsMyFilePaths.push("blah1".to_string());
    vsMyFilePaths.push("blah2".to_string());
    vsMyFilePaths.push("blah3".to_string());
    
    task::block_on(say_hi(&path1, &path2, &mut vsMyFilePaths))
}