Add paginated episodes

[jcs224]

Some podcasts have a pagination standard. Here's an example:

<atom:link href="https://changelog.com/podcast/feed" rel="self" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed" rel="first" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed?page=4" rel="last" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed?page=2" rel="next" type="application/rss+xml"/>

Page 2 looks like this:

<atom:link href="https://changelog.com/podcast/feed" rel="self" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed" rel="first" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed?page=4" rel="last" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed?page=1" rel="previous" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed?page=3" rel="next" type="application/rss+xml"/>

Last page:

<atom:link href="https://changelog.com/podcast/feed" rel="self" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed" rel="first" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed?page=4" rel="last" type="application/rss+xml"/>
<atom:link href="https://changelog.com/podcast/feed?page=3" rel="previous" type="application/rss+xml"/>

This particular podcast is actually not quite correct (rel="self" should indicate the current page, this one just lists the first page all the time) but there is enough metadata to handle pagination correctly, i.e. by checking for the presence of a rel="next" on each page.