refactor all to async/await (#617)

Co-authored-by: Danny Browning <danny.browning@protectwise.com>
Co-authored-by: Daniel Eades <danieleades@hotmail.com>

examples/simple.rs

@@ -1,6 +1,5 @@
-#![deny(warnings)]
-
 //! `cargo run --example simple`
+#![deny(warnings)]
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     env_logger::init();
@@ -13,7 +12,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     println!("Headers:\n{:?}", res.headers());
 
     // copy the response body directly to stdout
-    std::io::copy(&mut res, &mut std::io::stdout())?;
+    res.copy_to(&mut std::io::stdout())?;
 
     println!("\n\nDone.");
     Ok(())