Implemented asVector3(), asPosition() and asLocation()

Squash merge, closes #973

src/pocketmine/level/Position.php

@@ -46,6 +46,15 @@ class Position extends Vector3{
 		return new Position($pos->x, $pos->y, $pos->z, $level);
 	}
 
+	/**
+	 * Return a Position instance
+	 * 
+	 * @return Position
+	 */
+	public function asPosition() : Position{
+		return new Position($this->x, $this->y, $this->z, $this->level);
+	}
+	
 	/**
 	 * Returns the target Level, or null if the target is not valid.
 	 * If a reference exists to a Level which is closed, the reference will be destroyed and null will be returned.