templates: add base URL for feed content

[jk-ozlabs]

Relative links in the entry content do not currently have a base URI, so will be resolved relative to the feed URI:

Given an entry with the content:

<a href="some-resource.bin">

And URIS of:

• entry: https://example.org/blog/some-entry/
• feed: https://example.org/atom.xml

The link URI will end up as:

https://example.org/some-resource.bin

rather than the URI that ends up resolved in the rendered page:

https://example.org/blog/some-entry/some-resource.bin

The atom and RSS formats allow for an xml:base attribute (itself specified in 1) to provide a base URI of a subset of a document. This change adds xml:base attributes to each entry, using the page permalink.

This gives us something equivalent to:

<entry>
 <content xml:base="https://example.org/blog/some-entry/">
  <![CDATA[
   <a href="some-resource.bin">
  ]]>
 </content>
</entry>

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The place to discuss new features is the forum: https://zola.discourse.group/
If you want to add a new feature, please open a thread there first in the feature requests section.

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Code changes

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[Keats]

Thanks!