Add function to filter by post id

go/blog/blog.go

		document.title = baseTitle + " (Posts tagged '" + tag + "')";
	}
	function filterId(id) {
		var articles = document.querySelectorAll("article");
		for (var i = 0; i < articles.length; i++) {
			var article = articles[i];
			if (article.id != id) {
				article.classList.add("does-not-match");
			}
		}
		document.title = baseTitle + " (Only post id '" + id + "')";
	}
	function clearFilter() {
		var articles = document.querySelectorAll("article.does-not-match");
		for (var i = 0; i < articles.length; i++) {