Add role mentioning (#385)

* Add role mentioning

* Add to docs

* Forgot to save again

lib/Structures/Role.js

@@ -166,6 +166,15 @@ var Role = (function () {
 		return this.client.removeUserFromRole.apply(this.client, [member, this, callback]);
 	};
 
+	Role.prototype.mention = function mention() {
+		if (this.mentionable) return "<@&" + this.id + ">";
+		return this.name;
+	};
+
+	Role.prototype.toString = function toString() {
+		return this.mention();
+	};
+
 	return Role;
 })();