Include flag context in excerpt (#294)

* Added avoid flag text to meta descriptions

* Moved meta description logic to a shortcode

* Fixing nunjucks syntax error in base template head

Co-authored-by: Oscar <ovlb@users.noreply.github.com>

11ty/shortcodes/metaDescriptionWithFlag.js

@@ -0,0 +1,16 @@
+module.exports = function(preview, flag = {}) {
+  const initialCap = function(text) {
+    return `${text[0].toUpperCase()}${text.slice(1)}`;
+  };
+
+  if (flag && flag.level === 'avoid') {
+    if (flag.text) {
+      return `${initialCap(
+        flag.level
+      )}: ${flag.text.toLowerCase()}. ${initialCap(preview)}`;
+    }
+    return `${initialCap(flag.level)}: ${preview}`;
+  }
+
+  return initialCap(preview);
+};