Added API for transferring players to other servers (#355)

* Added API method `Player->transfer()` and PlayerTransferEvent

src/pocketmine/event/player/PlayerTransferEvent.php

@@ -0,0 +1,66 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\event\player;
+
+use pocketmine\event\Cancellable;
+use pocketmine\Player;
+
+class PlayerTransferEvent extends PlayerEvent implements Cancellable{
+	public static $handlerList = null;
+
+	protected $address;
+	protected $port = 19132;
+	protected $message;
+
+	public function __construct(Player $player, string $address, int $port, string $message){
+		$this->player = $player;
+		$this->address = $address;
+		$this->port = $port;
+		$this->message = $message;
+	}
+
+	public function getAddress() : string{
+		return $this->address;
+	}
+
+	public function setAddress(string $address){
+		$this->address = $address;
+	}
+
+	public function getPort() : int{
+		return $this->port;
+	}
+
+	public function setPort(int $port){
+		$this->port = $port;
+	}
+
+	public function getMessage() : string{
+		return $this->message;
+	}
+
+	public function setMessage(string $message){
+		$this->message = $message;
+	}
+}