This plugin finds enclosures from $entry->body by finding 1)
<B><a>B> links with rel=enclosure attribute, 2) <B><a>B>
links to any URL which filename extensions match with known
audio/video formats and 3) src attributes in <B><img>B> and <B><embed>B> tags.
Listen to the <a href="http://example.com/foobar.mp3">Podcast</a> now, or <a rel="enclosure"
href="http://example.com/foobar.m4a">download AAC version</a>. <img src="/img/logo.gif" />
Those 3 links (foobar.mp3, foobar.m4a and logo.gif) are
extracted as enclosures, while logo.gif is marked as inline, so
that they wont appear as enclosures in Publish::Feed.
You might want to also use Filter::HEADEnclosureMetadata plugin to
know the actual length (bytes-length) of enclosures by sending HEAD