proto: Refactor Request struct

Fixes #4

src/proto/req.rs

@@ -1,3 +0,0 @@
-use imap_codec::types::command::Command;
-
-pub type Request = Command;

src/proto/req/mod.rs

@@ -0,0 +1,5 @@
+use imap_codec::types::command::Command;
+
+pub struct Request {
+    pub command: Command,
+}

src/server/conn.rs

@@ -157,7 +157,7 @@ where
     fn call(&mut self, req: Request) -> Self::Future {
         use futures::{FutureExt, TryFutureExt};
 
-        let tag = req.tag.clone();
+        let tag = req.command.tag.clone();
 
         self.inner.call(req).map_ok(|res| (Some(tag), res)).boxed()
     }

src/server/pipeline.rs

@@ -67,7 +67,7 @@ where
 
             *this.read_buf = input.into();
 
-            let req = command;
+            let req = Request { command };
             return Poll::Ready(Some(Ok(req)));
         }
     }