Typehinted up entity API

Did you guys think ALPHA7 changes were done?!
Sone stuff still needs some work, most notably data-properties can't be typed yet because they are just mushed into a couple of methods.

src/pocketmine/entity/Animal.php

@@ -26,7 +26,7 @@ namespace pocketmine\entity;
 
 abstract class Animal extends Creature implements Ageable{
 
-	public function isBaby(){
+	public function isBaby() : bool{
 		return $this->getDataFlag(self::DATA_FLAGS, self::DATA_FLAG_BABY);
 	}
 }