collect all clients to one single folder (#119)

examples/pub.rs

@@ -17,12 +17,12 @@
 
 #![warn(rust_2018_idioms)]
 
-use mini_redis::{client, Result};
+use mini_redis::{clients::Client, Result};
 
 #[tokio::main]
 async fn main() -> Result<()> {
     // Open a connection to the mini-redis address.
-    let mut client = client::connect("127.0.0.1:6379").await?;
+    let mut client = Client::connect("127.0.0.1:6379").await?;
 
     // publish message `bar` on channel foo
     client.publish("foo", "bar".into()).await?;