Highlight recent post dates on homepage and article metadata (#793)

- Display post dates on homepage.

This helps make recent articles more noticeable. The highlight is applied
to post dates less than 48 hours old on the client side.

_includes/footer.html

@@ -82,6 +82,13 @@
 			hljs.highlightBlock(block);
 		});
 
+		document.querySelectorAll('[data-post-date]').forEach((postDate) => {
+			// Highlight post dates that are less than 48 hours old.
+			if (Date.parse(postDate.dataset.postDate) > (Date.now() - 1000 * 60 * 60 * 96)) {
+				postDate.classList.add("post-recent-highlight");
+			};
+		});
+
 		// Initialize lightbox.
 		new Tobii({
 			zoom: false,