Added support for setTimeZone grabbed from ISO8601 format

When a iso8601 format time with timezone is give `2013-12-31T12:30:00+0600` then make it automatically set the timezone to `+0600`.

Prevents format errors in `startOf` and `endOf` week examples like below

```
$iso8601 = '2014-11-02T05:12:15+05:30';

$moment = new \Moment\Moment($iso8601);
echo $moment->startOf('week')->format('d M').' - '.$moment->endOf('week')->format('d M');
```