Implement case-mapping for buffers and message handler

lib/client.js

@@ -434,6 +434,10 @@ export default class Client extends EventTarget {
 		}
 	}
 
+	isMyNick(nick) {
+		return this.cm(nick) == this.cm(this.nick);
+	}
+
 	/* Execute a command that expects a response. `done` is called with message
 	 * events until it returns a truthy value. */
 	roundtrip(msg, done) {