add cli for server/client (#4)

This PR adds a CLI to main.rs that allows you to run the redis server and eventually the redis client.

src/bin/server.rs

@@ -0,0 +1,17 @@
+use clap::Clap;
+use mini_redis::{server, DEFAULT_PORT};
+use std::io;
+
+#[tokio::main]
+pub async fn main() -> io::Result<()> {
+    let cli = Cli::parse();
+    let port = cli.port.unwrap_or(DEFAULT_PORT.to_string());
+    server::run(&port).await
+}
+
+#[derive(Clap, Debug)]
+#[clap(name = "mini-redis-server", version = env!("CARGO_PKG_VERSION"), author = env!("CARGO_PKG_AUTHORS"), about = "A Redis server")]
+struct Cli {
+    #[clap(name = "port", long = "--port")]
+    port: Option<String>,
+}