create a dedicated Message struct and implement reply(&str) on there, since it seems to be a commonly used thing. Begin implementing helpers for command parsing.

src/event/mod.rs

@@ -1,7 +1,7 @@
-use {Channel, User};
+use {Message, Channel, User};
 
 pub enum Event {
-    Message { sender: User, channel: Option<Channel>, content: String },
+    Message { message: Message },
     Join { channel: Channel },
     Quit { channel: Channel }
 }