fix HTTP response format and improve connection logging

Now curl helps debug invalid requests, hell yeah.

src/server.rs

@@ -77,7 +77,13 @@ async fn handle_connection(
         }
     };
 
-    stream.write_all(response.as_bytes()).await?;
+    let http_response = format!(
+        "HTTP/1.1 200 OK\r\nContent-Length: {}\r\n\r\n{}",
+        response.len(),
+        response
+    );
+    stream.write_all(http_response.as_bytes()).await?;
+
     Ok(())
 }