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

Squash merge, closes #973

src/pocketmine/math/Vector3.php

@@ -157,6 +157,15 @@ class Vector3{
 		}
 	}
 
+	/**
+	 * Return a Vector3 instance
+	 * 
+	 * @return Vector3
+	 */
+	public function asVector3() : Vector3{
+		return new Vector3($this->x, $this->y, $this->z);
+	}
+
 	/**
 	 * Returns the Vector3 side number opposite the specified one
 	 *