Support for multiple enclosures

[w3stling]

Add support for multiple enclosures per RSS Item.

<rss>
   ...
   <item>
      ...
      <enclosure url="https://url1" length="1" type="image/jpeg" />
      <enclosure url="https://url2" length="2" type="image/png" />
      <enclosure url="https://url3" length="3" type="image/gif" />
   </item>
   ...
</rss>

Method in Item class getting multiple enclosures:

List<Enclosure> enclosures = item.getEnclosures();