feat: update implementation of RSS feeds

Adds a new filter `convertRelativeLinks` that converts any relative link
to an absolute path
Adds an XML transform to minify the final output for smaller filesizes
Updates some data in meta
Adds a new macro for generating an RSS feed

config/transforms/xml-config.js

@@ -0,0 +1,12 @@
+import minifyXML from "minify-xml";
+
+export default function (eleventyConfig) {
+  eleventyConfig.addTransform("xml-minify", (content, path) => {
+    if (path && path.endsWith(".xml")) {
+      return minifyXML(content, {
+        shortenNamespaces: false,
+      });
+    }
+    return content;
+  });
+}