Added leave server and other stuff

lib/Client/Client.js

@@ -251,6 +251,20 @@ var Client = (function (_EventEmitter) {
 		});
 	};
 
+	Client.prototype.leaveServer = function leaveServer(server) {
+		var callback = arguments.length <= 1 || arguments[1] === undefined ? function (err) {} : arguments[1];
+
+		var self = this;
+		return new Promise(function (resolve, reject) {
+
+			self.internal.leaveServer(server).then(function () {
+				callback();resolve();
+			})["catch"](function (e) {
+				callback(e);reject(e);
+			});
+		});
+	};
+
 	return Client;
 })(EventEmitter);