Bug: XML entities in the ox-rss exporter

[Arun Isaac <theroarofthedragon@gmail.com>]

The ox-rss exporter does not replace characters (such as < , > , etc.)
by their corresponding XML entities (&lt; , &gt; , etc.) in the <title>
field of the generated XML.

For example, the following org file, when exported, will produce invalid
XML where the <title> field still contains the disallowed "<" character.

----- org file begins here -----
* Foo <- Bar

Some text
----- org file ends here -----

I'm guessing the ox-rss backend similarly fails to handle XML entities
in other fields as well.

I can provide a patch for this. But, do I use an external library like
xmlgen (https://github.com/philjackson/xmlgen), or do I write my own
find and replace functions like those in ox-html? I think the xmlgen
based approach provides better abstraction and avoids reinventing XML
generation. But, it will introduce an additional dependency.

Please provide thoughts and suggestions.

Thank you,
Arun Isaac.