Switch to non-blocking asynchronous I/O with async_std

* main: add a basic main loop and make the network part async
 * keypair: do not block when writing the generated keyfile
 * keypair: Read the secret file asynchronously

src/main.rs

@@ -1,6 +1,7 @@
 use clap::{load_yaml, App};
 use ed25519_dalek::Keypair;
 
+use async_std::fs;
 use async_std::net::UdpSocket;
 use async_std::path::PathBuf;
 
@@ -44,7 +45,7 @@ async fn main() -> std::io::Result<()> {
             .join("cosmoline")
             .join("config.toml")),
     };
-    let config = async_std::fs::read_to_string(config_file).await?;
+    let config = fs::read_to_string(config_file).await?;
     let config: Config = toml::from_str(config.as_str()).unwrap();
 
     let path = match options.value_of("path") {
@@ -57,7 +58,7 @@ async fn main() -> std::io::Result<()> {
     let keypair = Keypair::read_or_generate(path.join("secret")).await;
     println!("{}", keypair.to_json().pretty(2));
 
-    let socket = UdpSocket::bind(":::8008").await?;
+    let socket = UdpSocket::bind("0.0.0.0:8008").await?;
     let mut buf = [0u8; 1024];
 
     loop {