Introduce State.handleMessage

Takes an IRC message, updates the state.

Doesn't yet handle all messages, this will be a step-by-step process.

lib/client.js

@@ -466,6 +466,11 @@ export default class Client extends EventTarget {
 		return this.cm(nick) == this.cm(this.nick);
 	}
 
+	isChannel(name) {
+		// TODO: use the ISUPPORT token if available
+		return irc.STD_CHANNEL_TYPES.indexOf(name[0]) >= 0;
+	}
+
 	setPingInterval(sec) {
 		clearInterval(this.pingIntervalID);
 		this.pingIntervalID = null;