Add @throws docs.

Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

src/pocketmine/Server.php

@@ -1029,6 +1029,8 @@ class Server{
 	 * @param bool  $forceUnload
 	 *
 	 * @return bool
+	 *
+	 * @throws \InvalidStateException
 	 */
 	public function unloadLevel(Level $level, $forceUnload = false){
 		if($level === $this->getDefaultLevel() and !$forceUnload){

src/pocketmine/level/Level.php

@@ -2497,6 +2497,8 @@ class Level implements ChunkManager, Metadatable{
 	 * @param bool $generate
 	 *
 	 * @return bool
+	 *
+	 * @throws \InvalidStateException
 	 */
 	public function loadChunk($x, $z, $generate = true){
 		if(isset($this->chunks[$index = Level::chunkHash($x, $z)])){

src/pocketmine/level/generator/Generator.php

@@ -81,6 +81,8 @@ abstract class Generator{
 	 * @param int   $z
 	 *
 	 * @return \SplFixedArray
+	 *
+	 * @throws \InvalidArgumentCountException
 	 */
 	public static function getFastNoise1D(Noise $noise, $xSize, $samplingRate, $x, $y, $z){
 		if($samplingRate === 0){
@@ -116,6 +118,9 @@ abstract class Generator{
 	 * @param int   $z
 	 *
 	 * @return \SplFixedArray
+	 *
+	 * @throws \InvalidArgumentException
+	 * @throws \InvalidArgumentCountException
 	 */
 	public static function getFastNoise2D(Noise $noise, $xSize, $zSize, $samplingRate, $x, $y, $z){
 		if($samplingRate === 0){
@@ -171,6 +176,9 @@ abstract class Generator{
 	 * @param int   $z
 	 *
 	 * @return \SplFixedArray
+	 *
+	 * @throws \InvalidArgumentException
+	 * @throws \InvalidArgumentCountException
 	 */
 	public static function getFastNoise3D(Noise $noise, $xSize, $ySize, $zSize, $xSamplingRate, $ySamplingRate, $zSamplingRate, $x, $y, $z){
 		if($xSamplingRate === 0){