bug: feed page crashes when one of the user inputted data has an ampersand (&)
When podcast author name contains "&" sign, xml feed generation raises `SimpleXMLElement::addChild(): unterminated entity reference`:
`APPPATH/Helpers/rss_helper.php`:
```
77 $channel->addChild('author', $podcast->publisher, $itunes_namespace);
```
**NB**: This probably applies to all XML fields.
issue