feat: Expose document tags as rss categories

Add to the rss feed one <cateogry /> per tag of the document.

https://www.rssboard.org/rss-specification#ltcategorygtSubelementOfLtitemgt

Author: vbfox

src/document.rs

@@ -10,6 +10,7 @@ use liquid::ValueView;
 use liquid::model::Value;
 use log::trace;
 use regex::Regex;
+use rss::Category;
 
 use crate::cobalt_model;
 use crate::cobalt_model::Minify;
@@ -84,6 +85,13 @@ impl Document {
             .guid(Some(guid))
             .pub_date(self.front.published_date.map(|date| date.to_rfc2822()))
             .description(self.description_to_str())
+            .categories(
+                self.front
+                    .tags
+                    .iter()
+                    .map(|c| Category::from(c.as_str()))
+                    .collect::<Vec<_>>(),
+            )
             .build();
         Ok(item)
     }

tests/cmd/rss.out/_dest/rss.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?><rss version="2.0"><channel><title>My blog!</title><link>http://example.com</link><description>Blog description</description><item><title>My fifth Blogpost!</title><link>http://example.com/posts/my-fifth-blogpost.html</link><description><![CDATA[<h1>My fifth Blogpost!</h1>
-]]></description><guid>http://example.com/posts/my-fifth-blogpost.html</guid><pubDate>Tue, 16 Feb 2016 10:00:00 +0100</pubDate></item><item><title>My first Blogpost</title><link>http://example.com/posts/my-first-blogpost.html</link><description><![CDATA[It's my first blog post]]></description><guid>http://example.com/posts/my-first-blogpost.html</guid><pubDate>Fri, 01 Jan 2016 21:00:00 +0100</pubDate></item><item><title>My fourth Blogpost</title><link>http://example.com/posts/my-fourth-blogpost.html</link><description><![CDATA[<h1>My fourth Blogpost</h1>
+]]></description><guid>http://example.com/posts/my-fifth-blogpost.html</guid><pubDate>Tue, 16 Feb 2016 10:00:00 +0100</pubDate></item><item><title>My first Blogpost</title><link>http://example.com/posts/my-first-blogpost.html</link><description><![CDATA[It's my first blog post]]></description><category>blog</category><category>first</category><guid>http://example.com/posts/my-first-blogpost.html</guid><pubDate>Fri, 01 Jan 2016 21:00:00 +0100</pubDate></item><item><title>My fourth Blogpost</title><link>http://example.com/posts/my-fourth-blogpost.html</link><description><![CDATA[<h1>My fourth Blogpost</h1>
 ]]></description><guid>http://example.com/posts/my-fourth-blogpost.html</guid><pubDate>Fri, 29 May 2015 23:00:00 +0100</pubDate></item><item><title>My third Blogpost</title><link>http://example.com/posts/my-third-blogpost.html</link><description><![CDATA[<h1>My third Blogpost</h1>
-]]></description><guid>http://example.com/posts/my-third-blogpost.html</guid><pubDate>Wed, 27 May 2015 23:00:00 +0100</pubDate></item><item><title>My second Blogpost</title><link>http://example.com/posts/my-second-blogpost.html</link><description><![CDATA[<h1>My second Blogpost</h1>
+]]></description><category>test</category><category>blogpost</category><guid>http://example.com/posts/my-third-blogpost.html</guid><pubDate>Wed, 27 May 2015 23:00:00 +0100</pubDate></item><item><title>My second Blogpost</title><link>http://example.com/posts/my-second-blogpost.html</link><description><![CDATA[<h1>My second Blogpost</h1>
 ]]></description><guid>http://example.com/posts/my-second-blogpost.html</guid><pubDate>Fri, 02 Jan 2015 10:00:00 +0100</pubDate></item></channel></rss>