add hello world example (#20)

Author: jxs

examples/hello_world.rs

@@ -1,4 +1,32 @@
+//! Hello world server.
+//!
+//! A simple client that connects to a mini-redis server, sets key "hello" with value "world",
+//! and gets it from the server after
+//!
+//! You can test this out by running:
+//!
+//!     cargo run --bin server
+//!
+//! And then in another terminal run:
+//!
+//!     cargo run --example hello_world
+
+#![warn(rust_2018_idioms)]
+
+use mini_redis::{client, Result};
+
 #[tokio::main]
-async fn main() {
-    unimplemented!();
+pub async fn main() -> Result<()> {
+    // Open a connection to the mini-redis address.
+    let mut client = client::connect("127.0.0.1:6379").await?;
+
+    // Set the key "hello" with value "world"
+    client.set("hello", "world".into()).await?;
+
+    // Get key "hello"
+    let result = client.get("hello").await?;
+
+    println!("got value from the server; success={:?}", result.is_some());
+
+    Ok(())
 }