default all feature flags to off (#1811)

Changes the set of `default` feature flags to `[]`. By default, only
core traits are included without specifying feature flags. This makes it
easier for users to pick the components they need.

For convenience, a `full` feature flag is included that includes all
components.

Tests are configured to require the `full` feature. Testing individual
feature flags will need to be moved to a separate crate.

Closes #1791

1 files changed, 4 insertions, 6 deletions

diff --git a/README.md b/README.md
index c2aa98af..75e6f264 100644
--- a/README.md
+++ b/README.md
@@ -54,15 +54,13 @@ an asynchronous application.
 
 A basic TCP echo server with Tokio:
 
-```rust
+```rust,no_run
 use tokio::net::TcpListener;
 use tokio::prelude::*;
-use std::net::SocketAddr;
 
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let addr = "127.0.0.1:8080".parse::<SocketAddr>()?;
-    let mut listener = TcpListener::bind(&addr).await?;
+    let mut listener = TcpListener::bind("127.0.0.1:8080").await?;
 
     loop {
         let (mut socket, _) = listener.accept().await?;
@@ -77,14 +75,14 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                     Ok(n) if n == 0 => return,
                     Ok(n) => n,
                     Err(e) => {
-                        println!("failed to read from socket; err = {:?}", e);
+                        eprintln!("failed to read from socket; err = {:?}", e);
                         return;
                     }
                 };
 
                 // Write the data back
                 if let Err(e) = socket.write_all(&buf[0..n]).await {
-                    println!("failed to write to socket; err = {:?}", e);
+                    eprintln!("failed to write to socket; err = {:?}", e);
                     return;
                 }
             }